RFC 2060 - Internet Message Access Protocol - Version 4rev1

Network Working Group M. Crispin
Request for Comments: 2060 University of Washington
Obsoletes: 1730 December 1996
Category: Standards Track
 INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
Status of this Memo
 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements. Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol. Distribution of this memo is unlimited.
Abstract
 The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1)
 allows a client to access and manipulate electronic mail messages on
 a server. IMAP4rev1 permits manipulation of remote message folders,
 called "mailboxes", in a way that is functionally equivalent to local
 mailboxes. IMAP4rev1 also provides the capability for an offline
 client to resynchronize with the server (see also [IMAP-DISC]).
 IMAP4rev1 includes operations for creating, deleting, and renaming
 mailboxes; checking for new messages; permanently removing messages;
 setting and clearing flags; [RFC-822] and [MIME-IMB] parsing;
 searching; and selective fetching of message attributes, texts, and
 portions thereof. Messages in IMAP4rev1 are accessed by the use of
 numbers. These numbers are either message sequence numbers or unique
 identifiers.
 IMAP4rev1 supports a single server. A mechanism for accessing
 configuration information to support multiple IMAP4rev1 servers is
 discussed in [ACAP].
 IMAP4rev1 does not specify a means of posting mail; this function is
 handled by a mail transfer protocol such as [SMTP].
 IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
 unpublished IMAP2bis protocols. In the course of the evolution of
 IMAP4rev1, some aspects in the earlier protocol have become obsolete.
 Obsolete commands, responses, and data formats which an IMAP4rev1
 implementation may encounter when used with an earlier implementation
 are described in [IMAP-OBSOLETE].
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RFC 2060 IMAP4rev1 December 1996
 Other compatibility issues with IMAP2bis, the most common variant of
 the earlier protocol, are discussed in [IMAP-COMPAT]. A full
 discussion of compatibility issues with rare (and presumed extinct)
 variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
 primarily of historical interest.
Table of Contents
IMAP4rev1 Protocol Specification .................................. 4
1. How to Read This Document ................................. 4
1.1. Organization of This Document ............................. 4
1.2. Conventions Used in This Document ......................... 4
2. Protocol Overview ......................................... 5
2.1. Link Level ................................................ 5
2.2. Commands and Responses .................................... 6
2.2.1. Client Protocol Sender and Server Protocol Receiver ....... 6
2.2.2. Server Protocol Sender and Client Protocol Receiver ....... 7
2.3. Message Attributes ........................................ 7
2.3.1. Message Numbers ........................................... 7
2.3.1.1. Unique Identifier (UID) Message Attribute ......... 7
2.3.1.2. Message Sequence Number Message Attribute ......... 9
2.3.2. Flags Message Attribute .................................... 9
2.3.3. Internal Date Message Attribute ........................... 10
2.3.4. [RFC-822] Size Message Attribute .......................... 11
2.3.5. Envelope Structure Message Attribute ...................... 11
2.3.6. Body Structure Message Attribute .......................... 11
2.4. Message Texts ............................................. 11
3. State and Flow Diagram .................................... 11
3.1. Non-Authenticated State ................................... 11
3.2. Authenticated State ....................................... 11
3.3. Selected State ............................................ 12
3.4. Logout State .............................................. 12
4. Data Formats .............................................. 12
4.1. Atom ...................................................... 13
4.2. Number .................................................... 13
4.3. String ..................................................... 13
4.3.1. 8-bit and Binary Strings .................................. 13
4.4. Parenthesized List ........................................ 14
4.5. NIL ....................................................... 14
5. Operational Considerations ................................ 14
5.1. Mailbox Naming ............................................ 14
5.1.1. Mailbox Hierarchy Naming .................................. 14
5.1.2. Mailbox Namespace Naming Convention ....................... 14
5.1.3. Mailbox International Naming Convention ................... 15
5.2. Mailbox Size and Message Status Updates ................... 16
5.3. Response when no Command in Progress ...................... 16
5.4. Autologout Timer .......................................... 16
5.5. Multiple Commands in Progress ............................. 17
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RFC 2060 IMAP4rev1 December 1996
6. Client Commands ........................................... 17
6.1. Client Commands - Any State ............................... 18
6.1.1. CAPABILITY Command ........................................ 18
6.1.2. NOOP Command .............................................. 19
6.1.3. LOGOUT Command ............................................ 20
6.2. Client Commands - Non-Authenticated State ................. 20
6.2.1. AUTHENTICATE Command ...................................... 21
6.2.2. LOGIN Command ............................................. 22
6.3. Client Commands - Authenticated State ..................... 22
6.3.1. SELECT Command ............................................ 23
6.3.2. EXAMINE Command ........................................... 24
6.3.3. CREATE Command ............................................ 25
6.3.4. DELETE Command ............................................ 26
6.3.5. RENAME Command ............................................ 27
6.3.6. SUBSCRIBE Command ......................................... 29
6.3.7. UNSUBSCRIBE Command ....................................... 30
6.3.8. LIST Command .............................................. 30
6.3.9. LSUB Command .............................................. 32
6.3.10. STATUS Command ............................................ 33
6.3.11. APPEND Command ............................................ 34
6.4. Client Commands - Selected State .......................... 35
6.4.1. CHECK Command ............................................. 36
6.4.2. CLOSE Command ............................................. 36
6.4.3. EXPUNGE Command ........................................... 37
6.4.4. SEARCH Command ............................................ 37
6.4.5. FETCH Command ............................................. 41
6.4.6. STORE Command ............................................. 45
6.4.7. COPY Command .............................................. 46
6.4.8. UID Command ............................................... 47
6.5. Client Commands - Experimental/Expansion .................. 48
6.5.1. X<atom> Command ........................................... 48
7. Server Responses .......................................... 48
7.1. Server Responses - Status Responses ....................... 49
7.1.1. OK Response ............................................... 51
7.1.2. NO Response ............................................... 51
7.1.3. BAD Response .............................................. 52
7.1.4. PREAUTH Response .......................................... 52
7.1.5. BYE Response .............................................. 52
7.2. Server Responses - Server and Mailbox Status .............. 53
7.2.1. CAPABILITY Response ....................................... 53
7.2.2. LIST Response .............................................. 54
7.2.3. LSUB Response ............................................. 55
7.2.4 STATUS Response ........................................... 55
7.2.5. SEARCH Response ........................................... 55
7.2.6. FLAGS Response ............................................ 56
7.3. Server Responses - Mailbox Size ........................... 56
7.3.1. EXISTS Response ........................................... 56
7.3.2. RECENT Response ........................................... 57
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RFC 2060 IMAP4rev1 December 1996
7.4. Server Responses - Message Status ......................... 57
7.4.1. EXPUNGE Response .......................................... 57
7.4.2. FETCH Response ............................................ 58
7.5. Server Responses - Command Continuation Request ........... 63
8. Sample IMAP4rev1 connection ............................... 63
9. Formal Syntax ............................................. 64
10. Author's Note ............................................. 74
11. Security Considerations ................................... 74
12. Author's Address .......................................... 75
Appendices ........................................................ 76
A. References ................................................ 76
B. Changes from RFC 1730 ..................................... 77
C. Key Word Index ............................................ 79
IMAP4rev1 Protocol Specification
. How to Read This Document
1.1. Organization of This Document
 This document is written from the point of view of the implementor of
 an IMAP4rev1 client or server. Beyond the protocol overview in
 section 2, it is not optimized for someone trying to understand the
 operation of the protocol. The material in sections 3 through 5
 provides the general context and definitions with which IMAP4rev1
 operates.
 Sections 6, 7, and 9 describe the IMAP commands, responses, and
 syntax, respectively. The relationships among these are such that it
 is almost impossible to understand any of them separately. In
 particular, do not attempt to deduce command syntax from the command
 section alone; instead refer to the Formal Syntax section.
1.2. Conventions Used in This Document
 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.
 The following terms are used in this document to signify the
 requirements of this specification.
 1) MUST, or the adjective REQUIRED, means that the definition is
 an absolute requirement of the specification.
 2) MUST NOT that the definition is an absolute prohibition of the
 specification.
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RFC 2060 IMAP4rev1 December 1996
 3) SHOULD means that there may exist valid reasons in particular
 circumstances to ignore a particular item, but the full
 implications MUST be understood and carefully weighed before
 choosing a different course.
 4) SHOULD NOT means that there may exist valid reasons in
 particular circumstances when the particular behavior is
 acceptable or even useful, but the full implications SHOULD be
 understood and the case carefully weighed before implementing
 any behavior described with this label.
 5) MAY, or the adjective OPTIONAL, means that an item is truly
 optional. One vendor may choose to include the item because a
 particular marketplace requires it or because the vendor feels
 that it enhances the product while another vendor may omit the
 same item. An implementation which does not include a
 particular option MUST be prepared to interoperate with another
 implementation which does include the option.
 "Can" is used instead of "may" when referring to a possible
 circumstance or situation, as opposed to an optional facility of
 the protocol.
 "User" is used to refer to a human user, whereas "client" refers
 to the software being run by the user.
 "Connection" refers to the entire sequence of client/server
 interaction from the initial establishment of the network
 connection until its termination. "Session" refers to the
 sequence of client/server interaction from the time that a mailbox
 is selected (SELECT or EXAMINE command) until the time that
 selection ends (SELECT or EXAMINE of another mailbox, CLOSE
 command, or connection termination).
 Characters are 7-bit US-ASCII unless otherwise specified. Other
 character sets are indicated using a "CHARSET", as described in
 [MIME-IMT] and defined in [CHARSET]. CHARSETs have important
 additional semantics in addition to defining character set; refer
 to these documents for more detail.
. Protocol Overview
2.1. Link Level
 The IMAP4rev1 protocol assumes a reliable data stream such as
 provided by TCP. When TCP is used, an IMAP4rev1 server listens on
 port 143.
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RFC 2060 IMAP4rev1 December 1996
2.2. Commands and Responses
 An IMAP4rev1 connection consists of the establishment of a
 client/server network connection, an initial greeting from the
 server, and client/server interactions. These client/server
 interactions consist of a client command, server data, and a server
 completion result response.
 All interactions transmitted by client and server are in the form of
 lines; that is, strings that end with a CRLF. The protocol receiver
 of an IMAP4rev1 client or server is either reading a line, or is
 reading a sequence of octets with a known count followed by a line.
2.2.1. Client Protocol Sender and Server Protocol Receiver
 The client command begins an operation. Each client command is
 prefixed with an identifier (typically a short alphanumeric string,
 e.g. A0001, A0002, etc.) called a "tag". A different tag is
 generated by the client for each command.
 There are two cases in which a line from the client does not
 represent a complete command. In one case, a command argument is
 quoted with an octet count (see the description of literal in String
 under Data Formats); in the other case, the command arguments require
 server feedback (see the AUTHENTICATE command). In either case, the
 server sends a command continuation request response if it is ready
 for the octets (if appropriate) and the remainder of the command.
 This response is prefixed with the token "+".
 Note: If, instead, the server detected an error in the command, it
 sends a BAD completion response with tag matching the command (as
 described below) to reject the command and prevent the client from
 sending any more of the command.
 It is also possible for the server to send a completion response
 for some other command (if multiple commands are in progress), or
 untagged data. In either case, the command continuation request
 is still pending; the client takes the appropriate action for the
 response, and reads another response from the server. In all
 cases, the client MUST send a complete command (including
 receiving all command continuation request responses and command
 continuations for the command) before initiating a new command.
 The protocol receiver of an IMAP4rev1 server reads a command line
 from the client, parses the command and its arguments, and transmits
 server data and a server command completion result response.
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RFC 2060 IMAP4rev1 December 1996
2.2.2. Server Protocol Sender and Client Protocol Receiver
 Data transmitted by the server to the client and status responses
 that do not indicate command completion are prefixed with the token
 "*", and are called untagged responses.
 Server data MAY be sent as a result of a client command, or MAY be
 sent unilaterally by the server. There is no syntactic difference
 between server data that resulted from a specific command and server
 data that were sent unilaterally.
 The server completion result response indicates the success or
 failure of the operation. It is tagged with the same tag as the
 client command which began the operation. Thus, if more than one
 command is in progress, the tag in a server completion response
 identifies the command to which the response applies. There are
 three possible server completion responses: OK (indicating success),
 NO (indicating failure), or BAD (indicating protocol error such as
 unrecognized command or command syntax error).
 The protocol receiver of an IMAP4rev1 client reads a response line
 from the server. It then takes action on the response based upon the
 first token of the response, which can be a tag, a "*", or a "+".
 A client MUST be prepared to accept any server response at all times.
 This includes server data that was not requested. Server data SHOULD
 be recorded, so that the client can reference its recorded copy
 rather than sending a command to the server to request the data. In
 the case of certain server data, the data MUST be recorded.
 This topic is discussed in greater detail in the Server Responses
 section.
2.3. Message Attributes
 In addition to message text, each message has several attributes
 associated with it. These attributes may be retrieved individually
 or in conjunction with other attributes or message texts.
2.3.1. Message Numbers
 Messages in IMAP4rev1 are accessed by one of two numbers; the unique
 identifier and the message sequence number.
2.3.1.1. Unique Identifier (UID) Message Attribute
 A 32-bit value assigned to each message, which when used with the
 unique identifier validity value (see below) forms a 64-bit value
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RFC 2060 IMAP4rev1 December 1996
 that is permanently guaranteed not to refer to any other message in
 the mailbox. Unique identifiers are assigned in a strictly ascending
 fashion in the mailbox; as each message is added to the mailbox it is
 assigned a higher UID than the message(s) which were added
 previously.
 Unlike message sequence numbers, unique identifiers are not
 necessarily contiguous. Unique identifiers also persist across
 sessions. This permits a client to resynchronize its state from a
 previous session with the server (e.g. disconnected or offline access
 clients); this is discussed further in [IMAP-DISC].
 Associated with every mailbox is a unique identifier validity value,
 which is sent in an UIDVALIDITY response code in an OK untagged
 response at mailbox selection time. If unique identifiers from an
 earlier session fail to persist to this session, the unique
 identifier validity value MUST be greater than the one used in the
 earlier session.
 Note: Unique identifiers MUST be strictly ascending in the mailbox
 at all times. If the physical message store is re-ordered by a
 non-IMAP agent, this requires that the unique identifiers in the
 mailbox be regenerated, since the former unique identifers are no
 longer strictly ascending as a result of the re-ordering. Another
 instance in which unique identifiers are regenerated is if the
 message store has no mechanism to store unique identifiers.
 Although this specification recognizes that this may be
 unavoidable in certain server environments, it STRONGLY ENCOURAGES
 message store implementation techniques that avoid this problem.
 Another cause of non-persistance is if the mailbox is deleted and
 a new mailbox with the same name is created at a later date, Since
 the name is the same, a client may not know that this is a new
 mailbox unless the unique identifier validity is different. A
 good value to use for the unique identifier validity value is a
 32-bit representation of the creation date/time of the mailbox.
 It is alright to use a constant such as 1, but only if it
 guaranteed that unique identifiers will never be reused, even in
 the case of a mailbox being deleted (or renamed) and a new mailbox
 by the same name created at some future time.
 The unique identifier of a message MUST NOT change during the
 session, and SHOULD NOT change between sessions. However, if it is
 not possible to preserve the unique identifier of a message in a
 subsequent session, each subsequent session MUST have a new unique
 identifier validity value that is larger than any that was used
 previously.
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RFC 2060 IMAP4rev1 December 1996
2.3.1.2. Message Sequence Number Message Attribute
 A relative position from 1 to the number of messages in the mailbox.
 This position MUST be ordered by ascending unique identifier. As
 each new message is added, it is assigned a message sequence number
 that is 1 higher than the number of messages in the mailbox before
 that new message was added.
 Message sequence numbers can be reassigned during the session. For
 example, when a message is permanently removed (expunged) from the
 mailbox, the message sequence number for all subsequent messages is
 decremented. Similarly, a new message can be assigned a message
 sequence number that was once held by some other message prior to an
 expunge.
 In addition to accessing messages by relative position in the
 mailbox, message sequence numbers can be used in mathematical
 calculations. For example, if an untagged "EXISTS 11" is received,
 and previously an untagged "8 EXISTS" was received, three new
 messages have arrived with message sequence numbers of 9, 10, and 11.
 Another example; if message 287 in a 523 message mailbox has UID
 12345, there are exactly 286 messages which have lesser UIDs and 236
 messages which have greater UIDs.
2.3.2. Flags Message Attribute
 A list of zero or more named tokens associated with the message. A
 flag is set by its addition to this list, and is cleared by its
 removal. There are two types of flags in IMAP4rev1. A flag of
 either type may be permanent or session-only.
 A system flag is a flag name that is pre-defined in this
 specification. All system flags begin with "\". Certain system
 flags (\Deleted and \Seen) have special semantics described
 elsewhere. The currently-defined system flags are:
 \Seen Message has been read
 \Answered Message has been answered
 \Flagged Message is "flagged" for urgent/special attention
 \Deleted Message is "deleted" for removal by later EXPUNGE
 \Draft Message has not completed composition (marked as a
 draft).
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RFC 2060 IMAP4rev1 December 1996
 \Recent Message is "recently" arrived in this mailbox. This
 session is the first session to have been notified
 about this message; subsequent sessions will not see
 \Recent set for this message. This flag can not be
 altered by the client.
 If it is not possible to determine whether or not
 this session is the first session to be notified
 about a message, then that message SHOULD be
 considered recent.
 If multiple connections have the same mailbox
 selected simultaneously, it is undefined which of
 these connections will see newly-arrives messages
 with \Recent set and which will see it without
 \Recent set.
 A keyword is defined by the server implementation. Keywords do
 not begin with "\". Servers MAY permit the client to define new
 keywords in the mailbox (see the description of the
 PERMANENTFLAGS response code for more information).
 A flag may be permanent or session-only on a per-flag basis.
 Permanent flags are those which the client can add or remove
 from the message flags permanently; that is, subsequent sessions
 will see any change in permanent flags. Changes to session
 flags are valid only in that session.
 Note: The \Recent system flag is a special case of a
 session flag. \Recent can not be used as an argument in a
 STORE command, and thus can not be changed at all.
2.3.3. Internal Date Message Attribute
 The internal date and time of the message on the server. This is not
 the date and time in the [RFC-822] header, but rather a date and time
 which reflects when the message was received. In the case of
 messages delivered via [SMTP], this SHOULD be the date and time of
 final delivery of the message as defined by [SMTP]. In the case of
 messages delivered by the IMAP4rev1 COPY command, this SHOULD be the
 internal date and time of the source message. In the case of
 messages delivered by the IMAP4rev1 APPEND command, this SHOULD be
 the date and time as specified in the APPEND command description.
 All other cases are implementation defined.
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RFC 2060 IMAP4rev1 December 1996
2.3.4. [RFC-822] Size Message Attribute
 The number of octets in the message, as expressed in [RFC-822]
 format.
2.3.5. Envelope Structure Message Attribute
 A parsed representation of the [RFC-822] envelope information (not to
 be confused with an [SMTP] envelope) of the message.
2.3.6. Body Structure Message Attribute
 A parsed representation of the [MIME-IMB] body structure information
 of the message.
2.4. Message Texts
 In addition to being able to fetch the full [RFC-822] text of a
 message, IMAP4rev1 permits the fetching of portions of the full
 message text. Specifically, it is possible to fetch the [RFC-822]
 message header, [RFC-822] message body, a [MIME-IMB] body part, or a
 [MIME-IMB] header.
. State and Flow Diagram
 An IMAP4rev1 server is in one of four states. Most commands are
 valid in only certain states. It is a protocol error for the client
 to attempt a command while the command is in an inappropriate state.
 In this case, a server will respond with a BAD or NO (depending upon
 server implementation) command completion result.
3.1. Non-Authenticated State
 In non-authenticated state, the client MUST supply authentication
 credentials before most commands will be permitted. This state is
 entered when a connection starts unless the connection has been pre-
 authenticated.
3.2. Authenticated State
 In authenticated state, the client is authenticated and MUST select a
 mailbox to access before commands that affect messages will be
 permitted. This state is entered when a pre-authenticated connection
 starts, when acceptable authentication credentials have been
 provided, or after an error in selecting a mailbox.
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RFC 2060 IMAP4rev1 December 1996
3.3. Selected State
 In selected state, a mailbox has been selected to access. This state
 is entered when a mailbox has been successfully selected.
3.4. Logout State
 In logout state, the connection is being terminated, and the server
 will close the connection. This state can be entered as a result of
 a client request or by unilateral server decision.
 +--------------------------------------+
 |initial connection and server greeting|
 +--------------------------------------+
 || (1) || (2) || (3)
 VV || ||
 +-----------------+ || ||
 |non-authenticated| || ||
 +-----------------+ || ||
 || (7) || (4) || ||
 || VV VV ||
 || +----------------+ ||
 || | authenticated |<=++ ||
 || +----------------+ || ||
 || || (7) || (5) || (6) ||
 || || VV || ||
 || || +--------+ || ||
 || || |selected|==++ ||
 || || +--------+ ||
 || || || (7) ||
 VV VV VV VV
 +--------------------------------------+
 | logout and close connection |
 +--------------------------------------+
 (1) connection without pre-authentication (OK greeting)
 (2) pre-authenticated connection (PREAUTH greeting)
 (3) rejected connection (BYE greeting)
 (4) successful LOGIN or AUTHENTICATE command
 (5) successful SELECT or EXAMINE command
 (6) CLOSE command, or failed SELECT or EXAMINE command
 (7) LOGOUT command, server shutdown, or connection closed
. Data Formats
 IMAP4rev1 uses textual commands and responses. Data in IMAP4rev1 can
 be in one of several forms: atom, number, string, parenthesized list,
 or NIL.
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RFC 2060 IMAP4rev1 December 1996
4.1. Atom
 An atom consists of one or more non-special characters.
4.2. Number
 A number consists of one or more digit characters, and represents a
 numeric value.
4.3. String
 A string is in one of two forms: literal and quoted string. The
 literal form is the general form of string. The quoted string form
 is an alternative that avoids the overhead of processing a literal at
 the cost of limitations of characters that can be used in a quoted
 string.
 A literal is a sequence of zero or more octets (including CR and LF),
 prefix-quoted with an octet count in the form of an open brace ("{"),
 the number of octets, close brace ("}"), and CRLF. In the case of
 literals transmitted from server to client, the CRLF is immediately
 followed by the octet data. In the case of literals transmitted from
 client to server, the client MUST wait to receive a command
 continuation request (described later in this document) before
 sending the octet data (and the remainder of the command).
 A quoted string is a sequence of zero or more 7-bit characters,
 excluding CR and LF, with double quote (<">) characters at each end.
 The empty string is represented as either "" (a quoted string with
 zero characters between double quotes) or as {0} followed by CRLF (a
 literal with an octet count of 0).
 Note: Even if the octet count is 0, a client transmitting a
 literal MUST wait to receive a command continuation request.
4.3.1. 8-bit and Binary Strings
 8-bit textual and binary mail is supported through the use of a
 [MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY
 transmit 8-bit or multi-octet characters in literals, but SHOULD do
 so only when the [CHARSET] is identified.
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RFC 2060 IMAP4rev1 December 1996
 Although a BINARY body encoding is defined, unencoded binary strings
 are not permitted. A "binary string" is any string with NUL
 characters. Implementations MUST encode binary data into a textual
 form such as BASE64 before transmitting the data. A string with an
 excessive amount of CTL characters MAY also be considered to be
 binary.
4.4. Parenthesized List
 Data structures are represented as a "parenthesized list"; a sequence
 of data items, delimited by space, and bounded at each end by
 parentheses. A parenthesized list can contain other parenthesized
 lists, using multiple levels of parentheses to indicate nesting.
 The empty list is represented as () -- a parenthesized list with no
 members.
4.5. NIL
 The special atom "NIL" represents the non-existence of a particular
 data item that is represented as a string or parenthesized list, as
 distinct from the empty string "" or the empty parenthesized list ().
. Operational Considerations
5.1. Mailbox Naming
 The interpretation of mailbox names is implementation-dependent.
 However, the case-insensitive mailbox name INBOX is a special name
 reserved to mean "the primary mailbox for this user on this server".
5.1.1. Mailbox Hierarchy Naming
 If it is desired to export hierarchical mailbox names, mailbox names
 MUST be left-to-right hierarchical using a single character to
 separate levels of hierarchy. The same hierarchy separator character
 is used for all levels of hierarchy within a single name.
5.1.2. Mailbox Namespace Naming Convention
 By convention, the first hierarchical element of any mailbox name
 which begins with "#" identifies the "namespace" of the remainder of
 the name. This makes it possible to disambiguate between different
 types of mailbox stores, each of which have their own namespaces.
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RFC 2060 IMAP4rev1 December 1996
 For example, implementations which offer access to USENET
 newsgroups MAY use the "#news" namespace to partition the USENET
 newsgroup namespace from that of other mailboxes. Thus, the
 comp.mail.misc newsgroup would have an mailbox name of
 "#news.comp.mail.misc", and the name "comp.mail.misc" could refer
 to a different object (e.g. a user's private mailbox).
5.1.3. Mailbox International Naming Convention
 By convention, international mailbox names are specified using a
 modified version of the UTF-7 encoding described in [UTF-7]. The
 purpose of these modifications is to correct the following problems
 with UTF-7:
 1) UTF-7 uses the "+" character for shifting; this conflicts with
 the common use of "+" in mailbox names, in particular USENET
 newsgroup names.
 2) UTF-7's encoding is BASE64 which uses the "/" character; this
 conflicts with the use of "/" as a popular hierarchy delimiter.
 3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
 the use of "\" as a popular hierarchy delimiter.
 4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
 the use of "~" in some servers as a home directory indicator.
 5) UTF-7 permits multiple alternate forms to represent the same
 string; in particular, printable US-ASCII chararacters can be
 represented in encoded form.
 In modified UTF-7, printable US-ASCII characters except for "&"
 represent themselves; that is, characters with octet values 0x20-0x25
 and 0x27-0x7e. The character "&" (0x26) is represented by the two-
 octet sequence "&-".
 All other characters (octet values 0x00-0x1f, 0x7f-0xff, and all
 Unicode 16-bit octets) are represented in modified BASE64, with a
 further modification from [UTF-7] that "," is used instead of "/".
 Modified BASE64 MUST NOT be used to represent any printing US-ASCII
 character which can represent itself.
 "&" is used to shift to modified BASE64 and "-" to shift back to US-
 ASCII. All names start in US-ASCII, and MUST end in US-ASCII (that
 is, a name that ends with a Unicode 16-bit octet MUST end with a "-
 ").
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 For example, here is a mailbox name which mixes English, Japanese,
 and Chinese text: ~peter/mail/&ZeVnLIqe-/&U,BTFw-
5.2. Mailbox Size and Message Status Updates
 At any time, a server can send data that the client did not request.
 Sometimes, such behavior is REQUIRED. For example, agents other than
 the server MAY add messages to the mailbox (e.g. new mail delivery),
 change the flags of message in the mailbox (e.g. simultaneous access
 to the same mailbox by multiple agents), or even remove messages from
 the mailbox. A server MUST send mailbox size updates automatically
 if a mailbox size change is observed during the processing of a
 command. A server SHOULD send message flag updates automatically,
 without requiring the client to request such updates explicitly.
 Special rules exist for server notification of a client about the
 removal of messages to prevent synchronization errors; see the
 description of the EXPUNGE response for more detail.
 Regardless of what implementation decisions a client makes on
 remembering data from the server, a client implementation MUST record
 mailbox size updates. It MUST NOT assume that any command after
 initial mailbox selection will return the size of the mailbox.
5.3. Response when no Command in Progress
 Server implementations are permitted to send an untagged response
 (except for EXPUNGE) while there is no command in progress. Server
 implementations that send such responses MUST deal with flow control
 considerations. Specifically, they MUST either (1) verify that the
 size of the data does not exceed the underlying transport's available
 window size, or (2) use non-blocking writes.
5.4. Autologout Timer
 If a server has an inactivity autologout timer, that timer MUST be of
 at least 30 minutes' duration. The receipt of ANY command from the
 client during that interval SHOULD suffice to reset the autologout
 timer.
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5.5. Multiple Commands in Progress
 The client MAY send another command without waiting for the
 completion result response of a command, subject to ambiguity rules
 (see below) and flow control constraints on the underlying data
 stream. Similarly, a server MAY begin processing another command
 before processing the current command to completion, subject to
 ambiguity rules. However, any command continuation request responses
 and command continuations MUST be negotiated before any subsequent
 command is initiated.
 The exception is if an ambiguity would result because of a command
 that would affect the results of other commands. Clients MUST NOT
 send multiple commands without waiting if an ambiguity would result.
 If the server detects a possible ambiguity, it MUST execute commands
 to completion in the order given by the client.
 The most obvious example of ambiguity is when a command would affect
 the results of another command; for example, a FETCH of a message's
 flags and a STORE of that same message's flags.
 A non-obvious ambiguity occurs with commands that permit an untagged
 EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
 since an untagged EXPUNGE response can invalidate sequence numbers in
 a subsequent command. This is not a problem for FETCH, STORE, or
 SEARCH commands because servers are prohibited from sending EXPUNGE
 responses while any of those commands are in progress. Therefore, if
 the client sends any command other than FETCH, STORE, or SEARCH, it
 MUST wait for a response before sending a command with message
 sequence numbers.
 For example, the following non-waiting command sequences are invalid:
 FETCH + NOOP + STORE
 STORE + COPY + FETCH
 COPY + COPY
 CHECK + FETCH
 The following are examples of valid non-waiting command sequences:
 FETCH + STORE + SEARCH + CHECK
 STORE + COPY + EXPUNGE
. Client Commands
 IMAP4rev1 commands are described in this section. Commands are
 organized by the state in which the command is permitted. Commands
 which are permitted in multiple states are listed in the minimum
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RFC 2060 IMAP4rev1 December 1996
 permitted state (for example, commands valid in authenticated and
 selected state are listed in the authenticated state commands).
 Command arguments, identified by "Arguments:" in the command
 descriptions below, are described by function, not by syntax. The
 precise syntax of command arguments is described in the Formal Syntax
 section.
 Some commands cause specific server responses to be returned; these
 are identified by "Responses:" in the command descriptions below.
 See the response descriptions in the Responses section for
 information on these responses, and the Formal Syntax section for the
 precise syntax of these responses. It is possible for server data to
 be transmitted as a result of any command; thus, commands that do not
 specifically require server data specify "no specific responses for
 this command" instead of "none".
 The "Result:" in the command description refers to the possible
 tagged status responses to a command, and any special interpretation
 of these status responses.
6.1. Client Commands - Any State
 The following commands are valid in any state: CAPABILITY, NOOP, and
 LOGOUT.
6.1.1. CAPABILITY Command
 Arguments: none
 Responses: REQUIRED untagged response: CAPABILITY
 Result: OK - capability completed
 BAD - command unknown or arguments invalid
 The CAPABILITY command requests a listing of capabilities that the
 server supports. The server MUST send a single untagged
 CAPABILITY response with "IMAP4rev1" as one of the listed
 capabilities before the (tagged) OK response. This listing of
 capabilities is not dependent upon connection state or user. It
 is therefore not necessary to issue a CAPABILITY command more than
 once in a connection.
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 A capability name which begins with "AUTH=" indicates that the
 server supports that particular authentication mechanism. All
 such names are, by definition, part of this specification. For
 example, the authorization capability for an experimental
 "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not
 "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".
 Other capability names refer to extensions, revisions, or
 amendments to this specification. See the documentation of the
 CAPABILITY response for additional information. No capabilities,
 beyond the base IMAP4rev1 set defined in this specification, are
 enabled without explicit client action to invoke the capability.
 See the section entitled "Client Commands -
 Experimental/Expansion" for information about the form of site or
 implementation-specific capabilities.
 Example: C: abcd CAPABILITY
 S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4
 S: abcd OK CAPABILITY completed
6.1.2. NOOP Command
 Arguments: none
 Responses: no specific responses for this command (but see below)
 Result: OK - noop completed
 BAD - command unknown or arguments invalid
 The NOOP command always succeeds. It does nothing.
 Since any command can return a status update as untagged data, the
 NOOP command can be used as a periodic poll for new messages or
 message status updates during a period of inactivity. The NOOP
 command can also be used to reset any inactivity autologout timer
 on the server.
 Example: C: a002 NOOP
 S: a002 OK NOOP completed
 . . .
 C: a047 NOOP
 S: * 22 EXPUNGE
 S: * 23 EXISTS
 S: * 3 RECENT
 S: * 14 FETCH (FLAGS (\Seen \Deleted))
 S: a047 OK NOOP completed
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RFC 2060 IMAP4rev1 December 1996
6.1.3. LOGOUT Command
 Arguments: none
 Responses: REQUIRED untagged response: BYE
 Result: OK - logout completed
 BAD - command unknown or arguments invalid
 The LOGOUT command informs the server that the client is done with
 the connection. The server MUST send a BYE untagged response
 before the (tagged) OK response, and then close the network
 connection.
 Example: C: A023 LOGOUT
 S: * BYE IMAP4rev1 Server logging out
 S: A023 OK LOGOUT completed
 (Server and client then close the connection)
6.2. Client Commands - Non-Authenticated State
 In non-authenticated state, the AUTHENTICATE or LOGIN command
 establishes authentication and enter authenticated state. The
 AUTHENTICATE command provides a general mechanism for a variety of
 authentication techniques, whereas the LOGIN command uses the
 traditional user name and plaintext password pair.
 Server implementations MAY allow non-authenticated access to certain
 mailboxes. The convention is to use a LOGIN command with the userid
 "anonymous". A password is REQUIRED. It is implementation-dependent
 what requirements, if any, are placed on the password and what access
 restrictions are placed on anonymous users.
 Once authenticated (including as anonymous), it is not possible to
 re-enter non-authenticated state.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in non-authenticated state:
 AUTHENTICATE and LOGIN.
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6.2.1. AUTHENTICATE Command
 Arguments: authentication mechanism name
 Responses: continuation data can be requested
 Result: OK - authenticate completed, now in authenticated state
 NO - authenticate failure: unsupported authentication
 mechanism, credentials rejected
 BAD - command unknown or arguments invalid,
 authentication exchange cancelled
 The AUTHENTICATE command indicates an authentication mechanism,
 such as described in [IMAP-AUTH], to the server. If the server
 supports the requested authentication mechanism, it performs an
 authentication protocol exchange to authenticate and identify the
 client. It MAY also negotiate an OPTIONAL protection mechanism
 for subsequent protocol interactions. If the requested
 authentication mechanism is not supported, the server SHOULD
 reject the AUTHENTICATE command by sending a tagged NO response.
 The authentication protocol exchange consists of a series of
 server challenges and client answers that are specific to the
 authentication mechanism. A server challenge consists of a
 command continuation request response with the "+" token followed
 by a BASE64 encoded string. The client answer consists of a line
 consisting of a BASE64 encoded string. If the client wishes to
 cancel an authentication exchange, it issues a line with a single
 "*". If the server receives such an answer, it MUST reject the
 AUTHENTICATE command by sending a tagged BAD response.
 A protection mechanism provides integrity and privacy protection
 to the connection. If a protection mechanism is negotiated, it is
 applied to all subsequent data sent over the connection. The
 protection mechanism takes effect immediately following the CRLF
 that concludes the authentication exchange for the client, and the
 CRLF of the tagged OK response for the server. Once the
 protection mechanism is in effect, the stream of command and
 response octets is processed into buffers of ciphertext. Each
 buffer is transferred over the connection as a stream of octets
 prepended with a four octet field in network byte order that
 represents the length of the following data. The maximum
 ciphertext buffer length is defined by the protection mechanism.
 Authentication mechanisms are OPTIONAL. Protection mechanisms are
 also OPTIONAL; an authentication mechanism MAY be implemented
 without any protection mechanism. If an AUTHENTICATE command
 fails with a NO response, the client MAY try another
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RFC 2060 IMAP4rev1 December 1996
 authentication mechanism by issuing another AUTHENTICATE command,
 or MAY attempt to authenticate by using the LOGIN command. In
 other words, the client MAY request authentication types in
 decreasing order of preference, with the LOGIN command as a last
 resort.
 Example: S: * OK KerberosV4 IMAP4rev1 Server
 C: A001 AUTHENTICATE KERBEROS_V4
 S: + AmFYig==
 C: BAcAQU5EUkVXLkNNVS5FRFUAOCAsho84kLN3/IJmrMG+25a4DT
 +nZImJjnTNHJUtxAA+o0KPKfHEcAFs9a3CL5Oebe/ydHJUwYFd
 WwuQ1MWiy6IesKvjL5rL9WjXUb9MwT9bpObYLGOKi1Qh
 S: + or//EoAADZI=
 C: DiAF5A4gA+oOIALuBkAAmw==
 S: A001 OK Kerberos V4 authentication successful
 Note: the line breaks in the first client answer are for editorial
 clarity and are not in real authenticators.
6.2.2. LOGIN Command
 Arguments: user name
 password
 Responses: no specific responses for this command
 Result: OK - login completed, now in authenticated state
 NO - login failure: user name or password rejected
 BAD - command unknown or arguments invalid
 The LOGIN command identifies the client to the server and carries
 the plaintext password authenticating this user.
 Example: C: a001 LOGIN SMITH SESAME
 S: a001 OK LOGIN completed
6.3. Client Commands - Authenticated State
 In authenticated state, commands that manipulate mailboxes as atomic
 entities are permitted. Of these commands, the SELECT and EXAMINE
 commands will select a mailbox for access and enter selected state.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 the following commands are valid in authenticated state: SELECT,
 EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
 STATUS, and APPEND.
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6.3.1. SELECT Command
 Arguments: mailbox name
 Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
 OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS
 Result: OK - select completed, now in selected state
 NO - select failure, now in authenticated state: no
 such mailbox, can't access mailbox
 BAD - command unknown or arguments invalid
 The SELECT command selects a mailbox so that messages in the
 mailbox can be accessed. Before returning an OK to the client,
 the server MUST send the following untagged data to the client:
 FLAGS Defined flags in the mailbox. See the description
 of the FLAGS response for more detail.
 <n> EXISTS The number of messages in the mailbox. See the
 description of the EXISTS response for more detail.
 <n> RECENT The number of messages with the \Recent flag set.
 See the description of the RECENT response for more
 detail.
 OK [UIDVALIDITY <n>]
 The unique identifier validity value. See the
 description of the UID command for more detail.
 to define the initial state of the mailbox at the client.
 The server SHOULD also send an UNSEEN response code in an OK
 untagged response, indicating the message sequence number of the
 first unseen message in the mailbox.
 If the client can not change the permanent state of one or more of
 the flags listed in the FLAGS untagged response, the server SHOULD
 send a PERMANENTFLAGS response code in an OK untagged response,
 listing the flags that the client can change permanently.
 Only one mailbox can be selected at a time in a connection;
 simultaneous access to multiple mailboxes requires multiple
 connections. The SELECT command automatically deselects any
 currently selected mailbox before attempting the new selection.
 Consequently, if a mailbox is selected and a SELECT command that
 fails is attempted, no mailbox is selected.
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RFC 2060 IMAP4rev1 December 1996
 If the client is permitted to modify the mailbox, the server
 SHOULD prefix the text of the tagged OK response with the
 "[READ-WRITE]" response code.
 If the client is not permitted to modify the mailbox but is
 permitted read access, the mailbox is selected as read-only, and
 the server MUST prefix the text of the tagged OK response to
 SELECT with the "[READ-ONLY]" response code. Read-only access
 through SELECT differs from the EXAMINE command in that certain
 read-only mailboxes MAY permit the change of permanent state on a
 per-user (as opposed to global) basis. Netnews messages marked in
 a server-based .newsrc file are an example of such per-user
 permanent state that can be modified with read-only mailboxes.
 Example: C: A142 SELECT INBOX
 S: * 172 EXISTS
 S: * 1 RECENT
 S: * OK [UNSEEN 12] Message 12 is first unseen
 S: * OK [UIDVALIDITY 3857529045] UIDs valid
 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
 S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
 S: A142 OK [READ-WRITE] SELECT completed
6.3.2. EXAMINE Command
 Arguments: mailbox name
 Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
 OPTIONAL OK untagged responses: UNSEEN, PERMANENTFLAGS
 Result: OK - examine completed, now in selected state
 NO - examine failure, now in authenticated state: no
 such mailbox, can't access mailbox
 BAD - command unknown or arguments invalid
 The EXAMINE command is identical to SELECT and returns the same
 output; however, the selected mailbox is identified as read-only.
 No changes to the permanent state of the mailbox, including
 per-user state, are permitted.
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RFC 2060 IMAP4rev1 December 1996
 The text of the tagged OK response to the EXAMINE command MUST
 begin with the "[READ-ONLY]" response code.
 Example: C: A932 EXAMINE blurdybloop
 S: * 17 EXISTS
 S: * 2 RECENT
 S: * OK [UNSEEN 8] Message 8 is first unseen
 S: * OK [UIDVALIDITY 3857529045] UIDs valid
 S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
 S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
 S: A932 OK [READ-ONLY] EXAMINE completed
6.3.3. CREATE Command
 Arguments: mailbox name
 Responses: no specific responses for this command
 Result: OK - create completed
 NO - create failure: can't create mailbox with that name
 BAD - command unknown or arguments invalid
 The CREATE command creates a mailbox with the given name. An OK
 response is returned only if a new mailbox with that name has been
 created. It is an error to attempt to create INBOX or a mailbox
 with a name that refers to an extant mailbox. Any error in
 creation will return a tagged NO response.
 If the mailbox name is suffixed with the server's hierarchy
 separator character (as returned from the server by a LIST
 command), this is a declaration that the client intends to create
 mailbox names under this name in the hierarchy. Server
 implementations that do not require this declaration MUST ignore
 it.
 If the server's hierarchy separator character appears elsewhere in
 the name, the server SHOULD create any superior hierarchical names
 that are needed for the CREATE command to complete successfully.
 In other words, an attempt to create "foo/bar/zap" on a server in
 which "/" is the hierarchy separator character SHOULD create foo/
 and foo/bar/ if they do not already exist.
 If a new mailbox is created with the same name as a mailbox which
 was deleted, its unique identifiers MUST be greater than any
 unique identifiers used in the previous incarnation of the mailbox
 UNLESS the new incarnation has a different unique identifier
 validity value. See the description of the UID command for more
 detail.
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RFC 2060 IMAP4rev1 December 1996
 Example: C: A003 CREATE owatagusiam/
 S: A003 OK CREATE completed
 C: A004 CREATE owatagusiam/blurdybloop
 S: A004 OK CREATE completed
 Note: the interpretation of this example depends on whether "/"
 was returned as the hierarchy separator from LIST. If "/" is the
 hierarchy separator, a new level of hierarchy named "owatagusiam"
 with a member called "blurdybloop" is created. Otherwise, two
 mailboxes at the same hierarchy level are created.
6.3.4. DELETE Command
 Arguments: mailbox name
 Responses: no specific responses for this command
 Result: OK - delete completed
 NO - delete failure: can't delete mailbox with that name
 BAD - command unknown or arguments invalid
 The DELETE command permanently removes the mailbox with the given
 name. A tagged OK response is returned only if the mailbox has
 been deleted. It is an error to attempt to delete INBOX or a
 mailbox name that does not exist.
 The DELETE command MUST NOT remove inferior hierarchical names.
 For example, if a mailbox "foo" has an inferior "foo.bar"
 (assuming "." is the hierarchy delimiter character), removing
 "foo" MUST NOT remove "foo.bar". It is an error to attempt to
 delete a name that has inferior hierarchical names and also has
 the \Noselect mailbox name attribute (see the description of the
 LIST response for more details).
 It is permitted to delete a name that has inferior hierarchical
 names and does not have the \Noselect mailbox name attribute. In
 this case, all messages in that mailbox are removed, and the name
 will acquire the \Noselect mailbox name attribute.
 The value of the highest-used unique identifier of the deleted
 mailbox MUST be preserved so that a new mailbox created with the
 same name will not reuse the identifiers of the former
 incarnation, UNLESS the new incarnation has a different unique
 identifier validity value. See the description of the UID command
 for more detail.
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RFC 2060 IMAP4rev1 December 1996
 Examples: C: A682 LIST "" *
 S: * LIST () "/" blurdybloop
 S: * LIST (\Noselect) "/" foo
 S: * LIST () "/" foo/bar
 S: A682 OK LIST completed
 C: A683 DELETE blurdybloop
 S: A683 OK DELETE completed
 C: A684 DELETE foo
 S: A684 NO Name "foo" has inferior hierarchical names
 C: A685 DELETE foo/bar
 S: A685 OK DELETE Completed
 C: A686 LIST "" *
 S: * LIST (\Noselect) "/" foo
 S: A686 OK LIST completed
 C: A687 DELETE foo
 S: A687 OK DELETE Completed
 C: A82 LIST "" *
 S: * LIST () "." blurdybloop
 S: * LIST () "." foo
 S: * LIST () "." foo.bar
 S: A82 OK LIST completed
 C: A83 DELETE blurdybloop
 S: A83 OK DELETE completed
 C: A84 DELETE foo
 S: A84 OK DELETE Completed
 C: A85 LIST "" *
 S: * LIST () "." foo.bar
 S: A85 OK LIST completed
 C: A86 LIST "" %
 S: * LIST (\Noselect) "." foo
 S: A86 OK LIST completed
6.3.5. RENAME Command
 Arguments: existing mailbox name
 new mailbox name
 Responses: no specific responses for this command
 Result: OK - rename completed
 NO - rename failure: can't rename mailbox with that name,
 can't rename to mailbox with that name
 BAD - command unknown or arguments invalid
 The RENAME command changes the name of a mailbox. A tagged OK
 response is returned only if the mailbox has been renamed. It is
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RFC 2060 IMAP4rev1 December 1996
 an error to attempt to rename from a mailbox name that does not
 exist or to a mailbox name that already exists. Any error in
 renaming will return a tagged NO response.
 If the name has inferior hierarchical names, then the inferior
 hierarchical names MUST also be renamed. For example, a rename of
 "foo" to "zap" will rename "foo/bar" (assuming "/" is the
 hierarchy delimiter character) to "zap/bar".
 The value of the highest-used unique identifier of the old mailbox
 name MUST be preserved so that a new mailbox created with the same
 name will not reuse the identifiers of the former incarnation,
 UNLESS the new incarnation has a different unique identifier
 validity value. See the description of the UID command for more
 detail.
 Renaming INBOX is permitted, and has special behavior. It moves
 all messages in INBOX to a new mailbox with the given name,
 leaving INBOX empty. If the server implementation supports
 inferior hierarchical names of INBOX, these are unaffected by a
 rename of INBOX.
 Examples: C: A682 LIST "" *
 S: * LIST () "/" blurdybloop
 S: * LIST (\Noselect) "/" foo
 S: * LIST () "/" foo/bar
 S: A682 OK LIST completed
 C: A683 RENAME blurdybloop sarasoop
 S: A683 OK RENAME completed
 C: A684 RENAME foo zowie
 S: A684 OK RENAME Completed
 C: A685 LIST "" *
 S: * LIST () "/" sarasoop
 S: * LIST (\Noselect) "/" zowie
 S: * LIST () "/" zowie/bar
 S: A685 OK LIST completed
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RFC 2060 IMAP4rev1 December 1996
 C: Z432 LIST "" *
 S: * LIST () "." INBOX
 S: * LIST () "." INBOX.bar
 S: Z432 OK LIST completed
 C: Z433 RENAME INBOX old-mail
 S: Z433 OK RENAME completed
 C: Z434 LIST "" *
 S: * LIST () "." INBOX
 S: * LIST () "." INBOX.bar
 S: * LIST () "." old-mail
 S: Z434 OK LIST completed
6.3.6. SUBSCRIBE Command
 Arguments: mailbox
 Responses: no specific responses for this command
 Result: OK - subscribe completed
 NO - subscribe failure: can't subscribe to that name
 BAD - command unknown or arguments invalid
 The SUBSCRIBE command adds the specified mailbox name to the
 server's set of "active" or "subscribed" mailboxes as returned by
 the LSUB command. This command returns a tagged OK response only
 if the subscription is successful.
 A server MAY validate the mailbox argument to SUBSCRIBE to verify
 that it exists. However, it MUST NOT unilaterally remove an
 existing mailbox name from the subscription list even if a mailbox
 by that name no longer exists.
 Note: this requirement is because some server sites may routinely
 remove a mailbox with a well-known name (e.g. "system-alerts")
 after its contents expire, with the intention of recreating it
 when new contents are appropriate.
 Example: C: A002 SUBSCRIBE #news.comp.mail.mime
 S: A002 OK SUBSCRIBE completed
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RFC 2060 IMAP4rev1 December 1996
6.3.7. UNSUBSCRIBE Command
 Arguments: mailbox name
 Responses: no specific responses for this command
 Result: OK - unsubscribe completed
 NO - unsubscribe failure: can't unsubscribe that name
 BAD - command unknown or arguments invalid
 The UNSUBSCRIBE command removes the specified mailbox name from
 the server's set of "active" or "subscribed" mailboxes as returned
 by the LSUB command. This command returns a tagged OK response
 only if the unsubscription is successful.
 Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime
 S: A002 OK UNSUBSCRIBE completed
6.3..8. LIST Command
 Arguments: reference name
 mailbox name with possible wildcards
 Responses: untagged responses: LIST
 Result: OK - list completed
 NO - list failure: can't list that reference or name
 BAD - command unknown or arguments invalid
 The LIST command returns a subset of names from the complete set
 of all names available to the client. Zero or more untagged LIST
 replies are returned, containing the name attributes, hierarchy
 delimiter, and name; see the description of the LIST reply for
 more detail.
 The LIST command SHOULD return its data quickly, without undue
 delay. For example, it SHOULD NOT go to excess trouble to
 calculate \Marked or \Unmarked status or perform other processing;
 if each name requires 1 second of processing, then a list of 1200
 names would take 20 minutes!
 An empty ("" string) reference name argument indicates that the
 mailbox name is interpreted as by SELECT. The returned mailbox
 names MUST match the supplied mailbox name pattern. A non-empty
 reference name argument is the name of a mailbox or a level of
 mailbox hierarchy, and indicates a context in which the mailbox
 name is interpreted in an implementation-defined manner.
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 An empty ("" string) mailbox name argument is a special request to
 return the hierarchy delimiter and the root name of the name given
 in the reference. The value returned as the root MAY be null if
 the reference is non-rooted or is null. In all cases, the
 hierarchy delimiter is returned. This permits a client to get the
 hierarchy delimiter even when no mailboxes by that name currently
 exist.
 The reference and mailbox name arguments are interpreted, in an
 implementation-dependent fashion, into a canonical form that
 represents an unambiguous left-to-right hierarchy. The returned
 mailbox names will be in the interpreted form.
 Any part of the reference argument that is included in the
 interpreted form SHOULD prefix the interpreted form. It SHOULD
 also be in the same form as the reference name argument. This
 rule permits the client to determine if the returned mailbox name
 is in the context of the reference argument, or if something about
 the mailbox argument overrode the reference argument. Without
 this rule, the client would have to have knowledge of the server's
 naming semantics including what characters are "breakouts" that
 override a naming context.
 For example, here are some examples of how references and mailbox
 names might be interpreted on a UNIX-based server:
 Reference Mailbox Name Interpretation
 ------------ ------------ --------------
 ~smith/Mail/ foo.* ~smith/Mail/foo.*
 archive/ % archive/%
 #news. comp.mail.* #news.comp.mail.*
 ~smith/Mail/ /usr/doc/foo /usr/doc/foo
 archive/ ~fred/Mail/* ~fred/Mail/*
 The first three examples demonstrate interpretations in the
 context of the reference argument. Note that "~smith/Mail" SHOULD
 NOT be transformed into something like "/u2/users/smith/Mail", or
 it would be impossible for the client to determine that the
 interpretation was in the context of the reference.
 The character "*" is a wildcard, and matches zero or more
 characters at this position. The character "%" is similar to "*",
 but it does not match a hierarchy delimiter. If the "%" wildcard
 is the last character of a mailbox name argument, matching levels
 of hierarchy are also returned. If these levels of hierarchy are
 not also selectable mailboxes, they are returned with the
 \Noselect mailbox name attribute (see the description of the LIST
 response for more details).
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 Server implementations are permitted to "hide" otherwise
 accessible mailboxes from the wildcard characters, by preventing
 certain characters or names from matching a wildcard in certain
 situations. For example, a UNIX-based server might restrict the
 interpretation of "*" so that an initial "/" character does not
 match.
 The special name INBOX is included in the output from LIST, if
 INBOX is supported by this server for this user and if the
 uppercase string "INBOX" matches the interpreted reference and
 mailbox name arguments with wildcards as described above. The
 criteria for omitting INBOX is whether SELECT INBOX will return
 failure; it is not relevant whether the user's real INBOX resides
 on this or some other server.
 Example: C: A101 LIST "" ""
 S: * LIST (\Noselect) "/" ""
 S: A101 OK LIST Completed
 C: A102 LIST #news.comp.mail.misc ""
 S: * LIST (\Noselect) "." #news.
 S: A102 OK LIST Completed
 C: A103 LIST /usr/staff/jones ""
 S: * LIST (\Noselect) "/" /
 S: A103 OK LIST Completed
 C: A202 LIST ~/Mail/ %
 S: * LIST (\Noselect) "/" ~/Mail/foo
 S: * LIST () "/" ~/Mail/meetings
 S: A202 OK LIST completed
6.3.9. LSUB Command
 Arguments: reference name
 mailbox name with possible wildcards
 Responses: untagged responses: LSUB
 Result: OK - lsub completed
 NO - lsub failure: can't list that reference or name
 BAD - command unknown or arguments invalid
 The LSUB command returns a subset of names from the set of names
 that the user has declared as being "active" or "subscribed".
 Zero or more untagged LSUB replies are returned. The arguments to
 LSUB are in the same form as those for LIST.
 A server MAY validate the subscribed names to see if they still
 exist. If a name does not exist, it SHOULD be flagged with the
 \Noselect attribute in the LSUB response. The server MUST NOT
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RFC 2060 IMAP4rev1 December 1996
 unilaterally remove an existing mailbox name from the subscription
 list even if a mailbox by that name no longer exists.
 Example: C: A002 LSUB "#news." "comp.mail.*"
 S: * LSUB () "." #news.comp.mail.mime
 S: * LSUB () "." #news.comp.mail.misc
 S: A002 OK LSUB completed
6.3.10. STATUS Command
 Arguments: mailbox name
 status data item names
 Responses: untagged responses: STATUS
 Result: OK - status completed
 NO - status failure: no status for that name
 BAD - command unknown or arguments invalid
 The STATUS command requests the status of the indicated mailbox.
 It does not change the currently selected mailbox, nor does it
 affect the state of any messages in the queried mailbox (in
 particular, STATUS MUST NOT cause messages to lose the \Recent
 flag).
 The STATUS command provides an alternative to opening a second
 IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
 query that mailbox's status without deselecting the current
 mailbox in the first IMAP4rev1 connection.
 Unlike the LIST command, the STATUS command is not guaranteed to
 be fast in its response. In some implementations, the server is
 obliged to open the mailbox read-only internally to obtain certain
 status information. Also unlike the LIST command, the STATUS
 command does not accept wildcards.
 The currently defined status data items that can be requested are:
 MESSAGES The number of messages in the mailbox.
 RECENT The number of messages with the \Recent flag set.
 UIDNEXT The next UID value that will be assigned to a new
 message in the mailbox. It is guaranteed that this
 value will not change unless new messages are added
 to the mailbox; and that it will change when new
 messages are added even if those new messages are
 subsequently expunged.
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RFC 2060 IMAP4rev1 December 1996
 UIDVALIDITY The unique identifier validity value of the
 mailbox.
 UNSEEN The number of messages which do not have the \Seen
 flag set.
 Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
 S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
 S: A042 OK STATUS completed
6.3.11. APPEND Command
 Arguments: mailbox name
 OPTIONAL flag parenthesized list
 OPTIONAL date/time string
 message literal
 Responses: no specific responses for this command
 Result: OK - append completed
 NO - append error: can't append to that mailbox, error
 in flags or date/time or message text
 BAD - command unknown or arguments invalid
 The APPEND command appends the literal argument as a new message
 to the end of the specified destination mailbox. This argument
 SHOULD be in the format of an [RFC-822] message. 8-bit characters
 are permitted in the message. A server implementation that is
 unable to preserve 8-bit data properly MUST be able to reversibly
 convert 8-bit APPEND data to 7-bit using a [MIME-IMB] content
 transfer encoding.
 Note: There MAY be exceptions, e.g. draft messages, in which
 required [RFC-822] header lines are omitted in the message literal
 argument to APPEND. The full implications of doing so MUST be
 understood and carefully weighed.
 If a flag parenthesized list is specified, the flags SHOULD be set in
 the resulting message; otherwise, the flag list of the resulting
 message is set empty by default.
 If a date_time is specified, the internal date SHOULD be set in the
 resulting message; otherwise, the internal date of the resulting
 message is set to the current date and time by default.
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RFC 2060 IMAP4rev1 December 1996
 If the append is unsuccessful for any reason, the mailbox MUST be
 restored to its state before the APPEND attempt; no partial appending
 is permitted.
 If the destination mailbox does not exist, a server MUST return an
 error, and MUST NOT automatically create the mailbox. Unless it is
 certain that the destination mailbox can not be created, the server
 MUST send the response code "[TRYCREATE]" as the prefix of the text
 of the tagged NO response. This gives a hint to the client that it
 can attempt a CREATE command and retry the APPEND if the CREATE is
 successful.
 If the mailbox is currently selected, the normal new mail actions
 SHOULD occur. Specifically, the server SHOULD notify the client
 immediately via an untagged EXISTS response. If the server does not
 do so, the client MAY issue a NOOP command (or failing that, a CHECK
 command) after one or more APPEND commands.
 Example: C: A003 APPEND saved-messages (\Seen) {310}
 C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
 C: From: Fred Foobar <foobar@Blurdybloop.COM>
 C: Subject: afternoon meeting
 C: To: mooch@owatagu.siam.edu
 C: Message-Id: <B27397-0100000@Blurdybloop.COM>
 C: MIME-Version: 1.0
 C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
 C:
 C: Hello Joe, do you think we can meet at 3:30 tomorrow?
 C:
 S: A003 OK APPEND completed
 Note: the APPEND command is not used for message delivery, because
 it does not provide a mechanism to transfer [SMTP] envelope
 information.
6.4. Client Commands - Selected State
 In selected state, commands that manipulate messages in a mailbox are
 permitted.
 In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
 and the authenticated state commands (SELECT, EXAMINE, CREATE,
 DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and
 APPEND), the following commands are valid in the selected state:
 CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID.
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RFC 2060 IMAP4rev1 December 1996
6.4.1. CHECK Command
 Arguments: none
 Responses: no specific responses for this command
 Result: OK - check completed
 BAD - command unknown or arguments invalid
 The CHECK command requests a checkpoint of the currently selected
 mailbox. A checkpoint refers to any implementation-dependent
 housekeeping associated with the mailbox (e.g. resolving the
 server's in-memory state of the mailbox with the state on its
 disk) that is not normally executed as part of each command. A
 checkpoint MAY take a non-instantaneous amount of real time to
 complete. If a server implementation has no such housekeeping
 considerations, CHECK is equivalent to NOOP.
 There is no guarantee that an EXISTS untagged response will happen
 as a result of CHECK. NOOP, not CHECK, SHOULD be used for new
 mail polling.
 Example: C: FXXZ CHECK
 S: FXXZ OK CHECK Completed
6.4.2. CLOSE Command
 Arguments: none
 Responses: no specific responses for this command
 Result: OK - close completed, now in authenticated state
 NO - close failure: no mailbox selected
 BAD - command unknown or arguments invalid
 The CLOSE command permanently removes from the currently selected
 mailbox all messages that have the \Deleted flag set, and returns
 to authenticated state from selected state. No untagged EXPUNGE
 responses are sent.
 No messages are removed, and no error is given, if the mailbox is
 selected by an EXAMINE command or is otherwise selected read-only.
 Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT
 command MAY be issued without previously issuing a CLOSE command.
 The SELECT, EXAMINE, and LOGOUT commands implicitly close the
 currently selected mailbox without doing an expunge. However,
 when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT
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RFC 2060 IMAP4rev1 December 1996
 sequence is considerably faster than an EXPUNGE-LOGOUT or
 EXPUNGE-SELECT because no untagged EXPUNGE responses (which the
 client would probably ignore) are sent.
 Example: C: A341 CLOSE
 S: A341 OK CLOSE completed
6.4.3. EXPUNGE Command
 Arguments: none
 Responses: untagged responses: EXPUNGE
 Result: OK - expunge completed
 NO - expunge failure: can't expunge (e.g. permission
 denied)
 BAD - command unknown or arguments invalid
 The EXPUNGE command permanently removes from the currently
 selected mailbox all messages that have the \Deleted flag set.
 Before returning an OK to the client, an untagged EXPUNGE response
 is sent for each message that is removed.
 Example: C: A202 EXPUNGE
 S: * 3 EXPUNGE
 S: * 3 EXPUNGE
 S: * 5 EXPUNGE
 S: * 8 EXPUNGE
 S: A202 OK EXPUNGE completed
 Note: in this example, messages 3, 4, 7, and 11 had the
 \Deleted flag set. See the description of the EXPUNGE
 response for further explanation.
6.4.4. SEARCH Command
 Arguments: OPTIONAL [CHARSET] specification
 searching criteria (one or more)
 Responses: REQUIRED untagged response: SEARCH
 Result: OK - search completed
 NO - search error: can't search that [CHARSET] or
 criteria
 BAD - command unknown or arguments invalid
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RFC 2060 IMAP4rev1 December 1996
 The SEARCH command searches the mailbox for messages that match
 the given searching criteria. Searching criteria consist of one
 or more search keys. The untagged SEARCH response from the server
 contains a listing of message sequence numbers corresponding to
 those messages that match the searching criteria.
 When multiple keys are specified, the result is the intersection
 (AND function) of all the messages that match those keys. For
 example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers
 to all deleted messages from Smith that were placed in the mailbox
 since February 1, 1994. A search key can also be a parenthesized
 list of one or more search keys (e.g. for use with the OR and NOT
 keys).
 Server implementations MAY exclude [MIME-IMB] body parts with
 terminal content media types other than TEXT and MESSAGE from
 consideration in SEARCH matching.
 The OPTIONAL [CHARSET] specification consists of the word
 "CHARSET" followed by a registered [CHARSET]. It indicates the
 [CHARSET] of the strings that appear in the search criteria.
 [MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in
 [RFC-822]/[MIME-IMB] headers, MUST be decoded before comparing
 text in a [CHARSET] other than US-ASCII. US-ASCII MUST be
 supported; other [CHARSET]s MAY be supported. If the server does
 not support the specified [CHARSET], it MUST return a tagged NO
 response (not a BAD).
 In all search keys that use strings, a message matches the key if
 the string is a substring of the field. The matching is case-
 insensitive.
 The defined search keys are as follows. Refer to the Formal
 Syntax section for the precise syntactic definitions of the
 arguments.
 <message set> Messages with message sequence numbers
 corresponding to the specified message sequence
 number set
 ALL All messages in the mailbox; the default initial
 key for ANDing.
 ANSWERED Messages with the \Answered flag set.
 BCC <string> Messages that contain the specified string in the
 envelope structure's BCC field.
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RFC 2060 IMAP4rev1 December 1996
 BEFORE <date> Messages whose internal date is earlier than the
 specified date.
 BODY <string> Messages that contain the specified string in the
 body of the message.
 CC <string> Messages that contain the specified string in the
 envelope structure's CC field.
 DELETED Messages with the \Deleted flag set.
 DRAFT Messages with the \Draft flag set.
 FLAGGED Messages with the \Flagged flag set.
 FROM <string> Messages that contain the specified string in the
 envelope structure's FROM field.
 HEADER <field-name> <string>
 Messages that have a header with the specified
 field-name (as defined in [RFC-822]) and that
 contains the specified string in the [RFC-822]
 field-body.
 KEYWORD <flag> Messages with the specified keyword set.
 LARGER <n> Messages with an [RFC-822] size larger than the
 specified number of octets.
 NEW Messages that have the \Recent flag set but not the
 \Seen flag. This is functionally equivalent to
 "(RECENT UNSEEN)".
 NOT <search-key>
 Messages that do not match the specified search
 key.
 OLD Messages that do not have the \Recent flag set.
 This is functionally equivalent to "NOT RECENT" (as
 opposed to "NOT NEW").
 ON <date> Messages whose internal date is within the
 specified date.
 OR <search-key1> <search-key2>
 Messages that match either search key.
 RECENT Messages that have the \Recent flag set.
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RFC 2060 IMAP4rev1 December 1996
 SEEN Messages that have the \Seen flag set.
 SENTBEFORE <date>
 Messages whose [RFC-822] Date: header is earlier
 than the specified date.
 SENTON <date> Messages whose [RFC-822] Date: header is within the
 specified date.
 SENTSINCE <date>
 Messages whose [RFC-822] Date: header is within or
 later than the specified date.
 SINCE <date> Messages whose internal date is within or later
 than the specified date.
 SMALLER <n> Messages with an [RFC-822] size smaller than the
 specified number of octets.
 SUBJECT <string>
 Messages that contain the specified string in the
 envelope structure's SUBJECT field.
 TEXT <string> Messages that contain the specified string in the
 header or body of the message.
 TO <string> Messages that contain the specified string in the
 envelope structure's TO field.
 UID <message set>
 Messages with unique identifiers corresponding to
 the specified unique identifier set.
 UNANSWERED Messages that do not have the \Answered flag set.
 UNDELETED Messages that do not have the \Deleted flag set.
 UNDRAFT Messages that do not have the \Draft flag set.
 UNFLAGGED Messages that do not have the \Flagged flag set.
 UNKEYWORD <flag>
 Messages that do not have the specified keyword
 set.
 UNSEEN Messages that do not have the \Seen flag set.
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RFC 2060 IMAP4rev1 December 1996
 Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
 S: * SEARCH 2 84 882
 S: A282 OK SEARCH completed
6.4.5. FETCH Command
 Arguments: message set
 message data item names
 Responses: untagged responses: FETCH
 Result: OK - fetch completed
 NO - fetch error: can't fetch that data
 BAD - command unknown or arguments invalid
 The FETCH command retrieves data associated with a message in the
 mailbox. The data items to be fetched can be either a single atom
 or a parenthesized list.
 The currently defined data items that can be fetched are:
 ALL Macro equivalent to: (FLAGS INTERNALDATE
 RFC822.SIZE ENVELOPE)
 BODY Non-extensible form of BODYSTRUCTURE.
 BODY[<section>]<<partial>>
 The text of a particular body section. The section
 specification is a set of zero or more part
 specifiers delimited by periods. A part specifier
 is either a part number or one of the following:
 HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, MIME, and
 TEXT. An empty section specification refers to the
 entire message, including the header.
 Every message has at least one part number.
 Non-[MIME-IMB] messages, and non-multipart
 [MIME-IMB] messages with no encapsulated message,
 only have a part 1.
 Multipart messages are assigned consecutive part
 numbers, as they occur in the message. If a
 particular part is of type message or multipart,
 its parts MUST be indicated by a period followed by
 the part number within that nested multipart part.
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RFC 2060 IMAP4rev1 December 1996
 A part of type MESSAGE/RFC822 also has nested part
 numbers, referring to parts of the MESSAGE part's
 body.
 The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and
 TEXT part specifiers can be the sole part specifier
 or can be prefixed by one or more numeric part
 specifiers, provided that the numeric part
 specifier refers to a part of type MESSAGE/RFC822.
 The MIME part specifier MUST be prefixed by one or
 more numeric part specifiers.
 The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT
 part specifiers refer to the [RFC-822] header of
 the message or of an encapsulated [MIME-IMT]
 MESSAGE/RFC822 message. HEADER.FIELDS and
 HEADER.FIELDS.NOT are followed by a list of
 field-name (as defined in [RFC-822]) names, and
 return a subset of the header. The subset returned
 by HEADER.FIELDS contains only those header fields
 with a field-name that matches one of the names in
 the list; similarly, the subset returned by
 HEADER.FIELDS.NOT contains only the header fields
 with a non-matching field-name. The field-matching
 is case-insensitive but otherwise exact. In all
 cases, the delimiting blank line between the header
 and the body is always included.
 The MIME part specifier refers to the [MIME-IMB]
 header for this part.
 The TEXT part specifier refers to the text body of
 the message, omitting the [RFC-822] header.
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RFC 2060 IMAP4rev1 December 1996
 Here is an example of a complex message
 with some of its part specifiers:
 HEADER ([RFC-822] header of the message)
 TEXT MULTIPART/MIXED
 1 TEXT/PLAIN
 2 APPLICATION/OCTET-STREAM
 3 MESSAGE/RFC822
 3.HEADER ([RFC-822] header of the message)
 3.TEXT ([RFC-822] text body of the message)
 3.1 TEXT/PLAIN
 3.2 APPLICATION/OCTET-STREAM
 4 MULTIPART/MIXED
 4.1 IMAGE/GIF
 4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
 4.2 MESSAGE/RFC822
 4.2.HEADER ([RFC-822] header of the message)
 4.2.TEXT ([RFC-822] text body of the message)
 4.2.1 TEXT/PLAIN
 4.2.2 MULTIPART/ALTERNATIVE
 4.2.2.1 TEXT/PLAIN
 4.2.2.2 TEXT/RICHTEXT
 It is possible to fetch a substring of the
 designated text. This is done by appending an open
 angle bracket ("<"), the octet position of the
 first desired octet, a period, the maximum number
 of octets desired, and a close angle bracket (">")
 to the part specifier. If the starting octet is
 beyond the end of the text, an empty string is
 returned.
 Any partial fetch that attempts to read beyond the
 end of the text is truncated as appropriate. A
 partial fetch that starts at octet 0 is returned as
 a partial fetch, even if this truncation happened.
 Note: this means that BODY[]<0.2048> of a
 1500-octet message will return BODY[]<0>
 with a literal of size 1500, not BODY[].
 Note: a substring fetch of a
 HEADER.FIELDS or HEADER.FIELDS.NOT part
 specifier is calculated after subsetting
 the header.
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RFC 2060 IMAP4rev1 December 1996
 The \Seen flag is implicitly set; if this causes
 the flags to change they SHOULD be included as part
 of the FETCH responses.
 BODY.PEEK[<section>]<<partial>>
 An alternate form of BODY[<section>] that does not
 implicitly set the \Seen flag.
 BODYSTRUCTURE The [MIME-IMB] body structure of the message. This
 is computed by the server by parsing the [MIME-IMB]
 header fields in the [RFC-822] header and
 [MIME-IMB] headers.
 ENVELOPE The envelope structure of the message. This is
 computed by the server by parsing the [RFC-822]
 header into the component parts, defaulting various
 fields as necessary.
 FAST Macro equivalent to: (FLAGS INTERNALDATE
 RFC822.SIZE)
 FLAGS The flags that are set for this message.
 FULL Macro equivalent to: (FLAGS INTERNALDATE
 RFC822.SIZE ENVELOPE BODY)
 INTERNALDATE The internal date of the message.
 RFC822 Functionally equivalent to BODY[], differing in the
 syntax of the resulting untagged FETCH data (RFC822
 is returned).
 RFC822.HEADER Functionally equivalent to BODY.PEEK[HEADER],
 differing in the syntax of the resulting untagged
 FETCH data (RFC822.HEADER is returned).
 RFC822.SIZE The [RFC-822] size of the message.
 RFC822.TEXT Functionally equivalent to BODY[TEXT], differing in
 the syntax of the resulting untagged FETCH data
 (RFC822.TEXT is returned).
 UID The unique identifier for the message.
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RFC 2060 IMAP4rev1 December 1996
 Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
 S: * 2 FETCH ....
 S: * 3 FETCH ....
 S: * 4 FETCH ....
 S: A654 OK FETCH completed
6.4.6. STORE Command
 Arguments: message set
 message data item name
 value for message data item
 Responses: untagged responses: FETCH
 Result: OK - store completed
 NO - store error: can't store that data
 BAD - command unknown or arguments invalid
 The STORE command alters data associated with a message in the
 mailbox. Normally, STORE will return the updated value of the
 data with an untagged FETCH response. A suffix of ".SILENT" in
 the data item name prevents the untagged FETCH, and the server
 SHOULD assume that the client has determined the updated value
 itself or does not care about the updated value.
 Note: regardless of whether or not the ".SILENT" suffix was
 used, the server SHOULD send an untagged FETCH response if a
 change to a message's flags from an external source is
 observed. The intent is that the status of the flags is
 determinate without a race condition.
 The currently defined data items that can be stored are:
 FLAGS <flag list>
 Replace the flags for the message with the
 argument. The new value of the flags are returned
 as if a FETCH of those flags was done.
 FLAGS.SILENT <flag list>
 Equivalent to FLAGS, but without returning a new
 value.
 +FLAGS <flag list>
 Add the argument to the flags for the message. The
 new value of the flags are returned as if a FETCH
 of those flags was done.
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RFC 2060 IMAP4rev1 December 1996
 +FLAGS.SILENT <flag list>
 Equivalent to +FLAGS, but without returning a new
 value.
 -FLAGS <flag list>
 Remove the argument from the flags for the message.
 The new value of the flags are returned as if a
 FETCH of those flags was done.
 -FLAGS.SILENT <flag list>
 Equivalent to -FLAGS, but without returning a new
 value.
 Example: C: A003 STORE 2:4 +FLAGS (\Deleted)
 S: * 2 FETCH FLAGS (\Deleted \Seen)
 S: * 3 FETCH FLAGS (\Deleted)
 S: * 4 FETCH FLAGS (\Deleted \Flagged \Seen)
 S: A003 OK STORE completed
6.4.7. COPY Command
 Arguments: message set
 mailbox name
 Responses: no specific responses for this command
 Result: OK - copy completed
 NO - copy error: can't copy those messages or to that
 name
 BAD - command unknown or arguments invalid
 The COPY command copies the specified message(s) to the end of the
 specified destination mailbox. The flags and internal date of the
 message(s) SHOULD be preserved in the copy.
 If the destination mailbox does not exist, a server SHOULD return
 an error. It SHOULD NOT automatically create the mailbox. Unless
 it is certain that the destination mailbox can not be created, the
 server MUST send the response code "[TRYCREATE]" as the prefix of
 the text of the tagged NO response. This gives a hint to the
 client that it can attempt a CREATE command and retry the COPY if
 the CREATE is successful.
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RFC 2060 IMAP4rev1 December 1996
 If the COPY command is unsuccessful for any reason, server
 implementations MUST restore the destination mailbox to its state
 before the COPY attempt.
 Example: C: A003 COPY 2:4 MEETING
 S: A003 OK COPY completed
6.4.8. UID Command
 Arguments: command name
 command arguments
 Responses: untagged responses: FETCH, SEARCH
 Result: OK - UID command completed
 NO - UID command error
 BAD - command unknown or arguments invalid
 The UID command has two forms. In the first form, it takes as its
 arguments a COPY, FETCH, or STORE command with arguments
 appropriate for the associated command. However, the numbers in
 the message set argument are unique identifiers instead of message
 sequence numbers.
 In the second form, the UID command takes a SEARCH command with
 SEARCH command arguments. The interpretation of the arguments is
 the same as with SEARCH; however, the numbers returned in a SEARCH
 response for a UID SEARCH command are unique identifiers instead
 of message sequence numbers. For example, the command UID SEARCH
 1:100 UID 443:557 returns the unique identifiers corresponding to
 the intersection of the message sequence number set 1:100 and the
 UID set 443:557.
 Message set ranges are permitted; however, there is no guarantee
 that unique identifiers be contiguous. A non-existent unique
 identifier within a message set range is ignored without any error
 message generated.
 The number after the "*" in an untagged FETCH response is always a
 message sequence number, not a unique identifier, even for a UID
 command response. However, server implementations MUST implicitly
 include the UID message data item as part of any FETCH response
 caused by a UID command, regardless of whether a UID was specified
 as a message data item to the FETCH.
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RFC 2060 IMAP4rev1 December 1996
 Example: C: A999 UID FETCH 4827313:4828442 FLAGS
 S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
 S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
 S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
 S: A999 UID FETCH completed
6.5. Client Commands - Experimental/Expansion
6.5.1. X<atom> Command
 Arguments: implementation defined
 Responses: implementation defined
 Result: OK - command completed
 NO - failure
 BAD - command unknown or arguments invalid
 Any command prefixed with an X is an experimental command.
 Commands which are not part of this specification, a standard or
 standards-track revision of this specification, or an IESG-
 approved experimental protocol, MUST use the X prefix.
 Any added untagged responses issued by an experimental command
 MUST also be prefixed with an X. Server implementations MUST NOT
 send any such untagged responses, unless the client requested it
 by issuing the associated experimental command.
 Example: C: a441 CAPABILITY
 S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4 XPIG-LATIN
 S: a441 OK CAPABILITY completed
 C: A442 XPIG-LATIN
 S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
 S: A442 OK XPIG-LATIN ompleted-cay
. Server Responses
 Server responses are in three forms: status responses, server data,
 and command continuation request. The information contained in a
 server response, identified by "Contents:" in the response
 descriptions below, is described by function, not by syntax. The
 precise syntax of server responses is described in the Formal Syntax
 section.
 The client MUST be prepared to accept any response at all times.
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 Status responses can be tagged or untagged. Tagged status responses
 indicate the completion result (OK, NO, or BAD status) of a client
 command, and have a tag matching the command.
 Some status responses, and all server data, are untagged. An
 untagged response is indicated by the token "*" instead of a tag.
 Untagged status responses indicate server greeting, or server status
 that does not indicate the completion of a command (for example, an
 impending system shutdown alert). For historical reasons, untagged
 server data responses are also called "unsolicited data", although
 strictly speaking only unilateral server data is truly "unsolicited".
 Certain server data MUST be recorded by the client when it is
 received; this is noted in the description of that data. Such data
 conveys critical information which affects the interpretation of all
 subsequent commands and responses (e.g. updates reflecting the
 creation or destruction of messages).
 Other server data SHOULD be recorded for later reference; if the
 client does not need to record the data, or if recording the data has
 no obvious purpose (e.g. a SEARCH response when no SEARCH command is
 in progress), the data SHOULD be ignored.
 An example of unilateral untagged server data occurs when the IMAP
 connection is in selected state. In selected state, the server
 checks the mailbox for new messages as part of command execution.
 Normally, this is part of the execution of every command; hence, a
 NOOP command suffices to check for new messages. If new messages are
 found, the server sends untagged EXISTS and RECENT responses
 reflecting the new size of the mailbox. Server implementations that
 offer multiple simultaneous access to the same mailbox SHOULD also
 send appropriate unilateral untagged FETCH and EXPUNGE responses if
 another agent changes the state of any message flags or expunges any
 messages.
 Command continuation request responses use the token "+" instead of a
 tag. These responses are sent by the server to indicate acceptance
 of an incomplete client command and readiness for the remainder of
 the command.
7.1. Server Responses - Status Responses
 Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD
 may be tagged or untagged. PREAUTH and BYE are always untagged.
 Status responses MAY include an OPTIONAL "response code". A response
 code consists of data inside square brackets in the form of an atom,
 possibly followed by a space and arguments. The response code
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RFC 2060 IMAP4rev1 December 1996
 contains additional information or status codes for client software
 beyond the OK/NO/BAD condition, and are defined when there is a
 specific action that a client can take based upon the additional
 information.
 The currently defined response codes are:
 ALERT The human-readable text contains a special alert
 that MUST be presented to the user in a fashion
 that calls the user's attention to the message.
 NEWNAME Followed by a mailbox name and a new mailbox name.
 A SELECT or EXAMINE is failing because the target
 mailbox name no longer exists because it was
 renamed to the new mailbox name. This is a hint to
 the client that the operation can succeed if the
 SELECT or EXAMINE is reissued with the new mailbox
 name.
 PARSE The human-readable text represents an error in
 parsing the [RFC-822] header or [MIME-IMB] headers
 of a message in the mailbox.
 PERMANENTFLAGS Followed by a parenthesized list of flags,
 indicates which of the known flags that the client
 can change permanently. Any flags that are in the
 FLAGS untagged response, but not the PERMANENTFLAGS
 list, can not be set permanently. If the client
 attempts to STORE a flag that is not in the
 PERMANENTFLAGS list, the server will either reject
 it with a NO reply or store the state for the
 remainder of the current session only. The
 PERMANENTFLAGS list can also include the special
 flag \*, which indicates that it is possible to
 create new keywords by attempting to store those
 flags in the mailbox.
 READ-ONLY The mailbox is selected read-only, or its access
 while selected has changed from read-write to
 read-only.
 READ-WRITE The mailbox is selected read-write, or its access
 while selected has changed from read-only to
 read-write.
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RFC 2060 IMAP4rev1 December 1996
 TRYCREATE An APPEND or COPY attempt is failing because the
 target mailbox does not exist (as opposed to some
 other reason). This is a hint to the client that
 the operation can succeed if the mailbox is first
 created by the CREATE command.
 UIDVALIDITY Followed by a decimal number, indicates the unique
 identifier validity value.
 UNSEEN Followed by a decimal number, indicates the number
 of the first message without the \Seen flag set.
 Additional response codes defined by particular client or server
 implementations SHOULD be prefixed with an "X" until they are
 added to a revision of this protocol. Client implementations
 SHOULD ignore response codes that they do not recognize.
7.1.1. OK Response
 Contents: OPTIONAL response code
 human-readable text
 The OK response indicates an information message from the server.
 When tagged, it indicates successful completion of the associated
 command. The human-readable text MAY be presented to the user as
 an information message. The untagged form indicates an
 information-only message; the nature of the information MAY be
 indicated by a response code.
 The untagged form is also used as one of three possible greetings
 at connection startup. It indicates that the connection is not
 yet authenticated and that a LOGIN command is needed.
 Example: S: * OK IMAP4rev1 server ready
 C: A001 LOGIN fred blurdybloop
 S: * OK [ALERT] System shutdown in 10 minutes
 S: A001 OK LOGIN Completed
7.1.2. NO Response
 Contents: OPTIONAL response code
 human-readable text
 The NO response indicates an operational error message from the
 server. When tagged, it indicates unsuccessful completion of the
 associated command. The untagged form indicates a warning; the
 command can still complete successfully. The human-readable text
 describes the condition.
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RFC 2060 IMAP4rev1 December 1996
 Example: C: A222 COPY 1:2 owatagusiam
 S: * NO Disk is 98% full, please delete unnecessary data
 S: A222 OK COPY completed
 C: A223 COPY 3:200 blurdybloop
 S: * NO Disk is 98% full, please delete unnecessary data
 S: * NO Disk is 99% full, please delete unnecessary data
 S: A223 NO COPY failed: disk is full
7.1.3. BAD Response
 Contents: OPTIONAL response code
 human-readable text
 The BAD response indicates an error message from the server. When
 tagged, it reports a protocol-level error in the client's command;
 the tag indicates the command that caused the error. The untagged
 form indicates a protocol-level error for which the associated
 command can not be determined; it can also indicate an internal
 server failure. The human-readable text describes the condition.
 Example: C: ...very long command line...
 S: * BAD Command line too long
 C: ...empty line...
 S: * BAD Empty command line
 C: A443 EXPUNGE
 S: * BAD Disk crash, attempting salvage to a new disk!
 S: * OK Salvage successful, no data lost
 S: A443 OK Expunge completed
7.1.4. PREAUTH Response
 Contents: OPTIONAL response code
 human-readable text
 The PREAUTH response is always untagged, and is one of three
 possible greetings at connection startup. It indicates that the
 connection has already been authenticated by external means and
 thus no LOGIN command is needed.
 Example: S: * PREAUTH IMAP4rev1 server logged in as Smith
7.1.5. BYE Response
 Contents: OPTIONAL response code
 human-readable text
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 The BYE response is always untagged, and indicates that the server
 is about to close the connection. The human-readable text MAY be
 displayed to the user in a status report by the client. The BYE
 response is sent under one of four conditions:
 1) as part of a normal logout sequence. The server will close
 the connection after sending the tagged OK response to the
 LOGOUT command.
 2) as a panic shutdown announcement. The server closes the
 connection immediately.
 3) as an announcement of an inactivity autologout. The server
 closes the connection immediately.
 4) as one of three possible greetings at connection startup,
 indicating that the server is not willing to accept a
 connection from this client. The server closes the
 connection immediately.
 The difference between a BYE that occurs as part of a normal
 LOGOUT sequence (the first case) and a BYE that occurs because of
 a failure (the other three cases) is that the connection closes
 immediately in the failure case.
 Example: S: * BYE Autologout; idle for too long
7.2. Server Responses - Server and Mailbox Status
 These responses are always untagged. This is how server and mailbox
 status data are transmitted from the server to the client. Many of
 these responses typically result from a command with the same name.
7.2.1. CAPABILITY Response
 Contents: capability listing
 The CAPABILITY response occurs as a result of a CAPABILITY
 command. The capability listing contains a space-separated
 listing of capability names that the server supports. The
 capability listing MUST include the atom "IMAP4rev1".
 A capability name which begins with "AUTH=" indicates that the
 server supports that particular authentication mechanism.
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RFC 2060 IMAP4rev1 December 1996
 Other capability names indicate that the server supports an
 extension, revision, or amendment to the IMAP4rev1 protocol.
 Server responses MUST conform to this document until the client
 issues a command that uses the associated capability.
 Capability names MUST either begin with "X" or be standard or
 standards-track IMAP4rev1 extensions, revisions, or amendments
 registered with IANA. A server MUST NOT offer unregistered or
 non-standard capability names, unless such names are prefixed with
 an "X".
 Client implementations SHOULD NOT require any capability name
 other than "IMAP4rev1", and MUST ignore any unknown capability
 names.
 Example: S: * CAPABILITY IMAP4rev1 AUTH=KERBEROS_V4 XPIG-LATIN
7.2.2. LIST Response
 Contents: name attributes
 hierarchy delimiter
 name
 The LIST response occurs as a result of a LIST command. It
 returns a single name that matches the LIST specification. There
 can be multiple LIST responses for a single LIST command.
 Four name attributes are defined:
 \Noinferiors It is not possible for any child levels of
 hierarchy to exist under this name; no child levels
 exist now and none can be created in the future.
 \Noselect It is not possible to use this name as a selectable
 mailbox.
 \Marked The mailbox has been marked "interesting" by the
 server; the mailbox probably contains messages that
 have been added since the last time the mailbox was
 selected.
 \Unmarked The mailbox does not contain any additional
 messages since the last time the mailbox was
 selected.
 If it is not feasible for the server to determine whether the
 mailbox is "interesting" or not, or if the name is a \Noselect
 name, the server SHOULD NOT send either \Marked or \Unmarked.
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RFC 2060 IMAP4rev1 December 1996
 The hierarchy delimiter is a character used to delimit levels of
 hierarchy in a mailbox name. A client can use it to create child
 mailboxes, and to search higher or lower levels of naming
 hierarchy. All children of a top-level hierarchy node MUST use
 the same separator character. A NIL hierarchy delimiter means
 that no hierarchy exists; the name is a "flat" name.
 The name represents an unambiguous left-to-right hierarchy, and
 MUST be valid for use as a reference in LIST and LSUB commands.
 Unless \Noselect is indicated, the name MUST also be valid as an
 argument for commands, such as SELECT, that accept mailbox
 names.
 Example: S: * LIST (\Noselect) "/" ~/Mail/foo
7.2.3. LSUB Response
 Contents: name attributes
 hierarchy delimiter
 name
 The LSUB response occurs as a result of an LSUB command. It
 returns a single name that matches the LSUB specification. There
 can be multiple LSUB responses for a single LSUB command. The
 data is identical in format to the LIST response.
 Example: S: * LSUB () "." #news.comp.mail.misc
7.2.4 STATUS Response
 Contents: name
 status parenthesized list
 The STATUS response occurs as a result of an STATUS command. It
 returns the mailbox name that matches the STATUS specification and
 the requested mailbox status information.
 Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
7.2.5. SEARCH Response
 Contents: zero or more numbers
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RFC 2060 IMAP4rev1 December 1996
 The SEARCH response occurs as a result of a SEARCH or UID SEARCH
 command. The number(s) refer to those messages that match the
 search criteria. For SEARCH, these are message sequence numbers;
 for UID SEARCH, these are unique identifiers. Each number is
 delimited by a space.
 Example: S: * SEARCH 2 3 6
7.2.6. FLAGS Response
 Contents: flag parenthesized list
 The FLAGS response occurs as a result of a SELECT or EXAMINE
 command. The flag parenthesized list identifies the flags (at a
 minimum, the system-defined flags) that are applicable for this
 mailbox. Flags other than the system flags can also exist,
 depending on server implementation.
 The update from the FLAGS response MUST be recorded by the client.
 Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
7.3. Server Responses - Mailbox Size
 These responses are always untagged. This is how changes in the size
 of the mailbox are trasnmitted from the server to the client.
 Immediately following the "*" token is a number that represents a
 message count.
7.3.1. EXISTS Response
 Contents: none
 The EXISTS response reports the number of messages in the mailbox.
 This response occurs as a result of a SELECT or EXAMINE command,
 and if the size of the mailbox changes (e.g. new mail).
 The update from the EXISTS response MUST be recorded by the
 client.
 Example: S: * 23 EXISTS
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RFC 2060 IMAP4rev1 December 1996
7.3.2. RECENT Response
 Contents: none
 The RECENT response reports the number of messages with the
 \Recent flag set. This response occurs as a result of a SELECT or
 EXAMINE command, and if the size of the mailbox changes (e.g. new
 mail).
 Note: It is not guaranteed that the message sequence numbers of
 recent messages will be a contiguous range of the highest n
 messages in the mailbox (where n is the value reported by the
 RECENT response). Examples of situations in which this is not
 the case are: multiple clients having the same mailbox open
 (the first session to be notified will see it as recent, others
 will probably see it as non-recent), and when the mailbox is
 re-ordered by a non-IMAP agent.
 The only reliable way to identify recent messages is to look at
 message flags to see which have the \Recent flag set, or to do
 a SEARCH RECENT.
 The update from the RECENT response MUST be recorded by the
 client.
 Example: S: * 5 RECENT
7.4. Server Responses - Message Status
 These responses are always untagged. This is how message data are
 transmitted from the server to the client, often as a result of a
 command with the same name. Immediately following the "*" token is a
 number that represents a message sequence number.
7.4.1. EXPUNGE Response
 Contents: none
 The EXPUNGE response reports that the specified message sequence
 number has been permanently removed from the mailbox. The message
 sequence number for each successive message in the mailbox is
 immediately decremented by 1, and this decrement is reflected in
 message sequence numbers in subsequent responses (including other
 untagged EXPUNGE responses).
 As a result of the immediate decrement rule, message sequence
 numbers that appear in a set of successive EXPUNGE responses
 depend upon whether the messages are removed starting from lower
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RFC 2060 IMAP4rev1 December 1996
 numbers to higher numbers, or from higher numbers to lower
 numbers. For example, if the last 5 messages in a 9-message
 mailbox are expunged; a "lower to higher" server will send five
 untagged EXPUNGE responses for message sequence number 5, whereas
 a "higher to lower server" will send successive untagged EXPUNGE
 responses for message sequence numbers 9, 8, 7, 6, and 5.
 An EXPUNGE response MUST NOT be sent when no command is in
 progress; nor while responding to a FETCH, STORE, or SEARCH
 command. This rule is necessary to prevent a loss of
 synchronization of message sequence numbers between client and
 server.
 The update from the EXPUNGE response MUST be recorded by the
 client.
 Example: S: * 44 EXPUNGE
7.4.2. FETCH Response
 Contents: message data
 The FETCH response returns data about a message to the client.
 The data are pairs of data item names and their values in
 parentheses. This response occurs as the result of a FETCH or
 STORE command, as well as by unilateral server decision (e.g. flag
 updates).
 The current data items are:
 BODY A form of BODYSTRUCTURE without extension data.
 BODY[<section>]<<origin_octet>>
 A string expressing the body contents of the
 specified section. The string SHOULD be
 interpreted by the client according to the content
 transfer encoding, body type, and subtype.
 If the origin octet is specified, this string is a
 substring of the entire body contents, starting at
 that origin octet. This means that BODY[]<0> MAY
 be truncated, but BODY[] is NEVER truncated.
 8-bit textual data is permitted if a [CHARSET]
 identifier is part of the body parameter
 parenthesized list for this section. Note that
 headers (part specifiers HEADER or MIME, or the
 header portion of a MESSAGE/RFC822 part), MUST be
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RFC 2060 IMAP4rev1 December 1996
 7-bit; 8-bit characters are not permitted in
 headers. Note also that the blank line at the end
 of the header is always included in header data.
 Non-textual data such as binary data MUST be
 transfer encoded into a textual form such as BASE64
 prior to being sent to the client. To derive the
 original binary data, the client MUST decode the
 transfer encoded string.
 BODYSTRUCTURE A parenthesized list that describes the [MIME-IMB]
 body structure of a message. This is computed by
 the server by parsing the [MIME-IMB] header fields,
 defaulting various fields as necessary.
 For example, a simple text message of 48 lines and
 2279 octets can have a body structure of: ("TEXT"
 "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 2279
 48)
 Multiple parts are indicated by parenthesis
 nesting. Instead of a body type as the first
 element of the parenthesized list there is a nested
 body. The second element of the parenthesized list
 is the multipart subtype (mixed, digest, parallel,
 alternative, etc.).
 For example, a two part message consisting of a
 text and a BASE645-encoded text attachment can have
 a body structure of: (("TEXT" "PLAIN" ("CHARSET"
 "US-ASCII") NIL NIL "7BIT" 1152 23)("TEXT" "PLAIN"
 ("CHARSET" "US-ASCII" "NAME" "cc.diff")
 "<960723163407.20117h@cac.washington.edu>"
 "Compiler diff" "BASE64" 4554 73) "MIXED"))
 Extension data follows the multipart subtype.
 Extension data is never returned with the BODY
 fetch, but can be returned with a BODYSTRUCTURE
 fetch. Extension data, if present, MUST be in the
 defined order.
 The extension data of a multipart body part are in
 the following order:
 body parameter parenthesized list
 A parenthesized list of attribute/value pairs
 [e.g. ("foo" "bar" "baz" "rag") where "bar" is
 the value of "foo" and "rag" is the value of
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RFC 2060 IMAP4rev1 December 1996
 "baz"] as defined in [MIME-IMB].
 body disposition
 A parenthesized list, consisting of a
 disposition type string followed by a
 parenthesized list of disposition
 attribute/value pairs. The disposition type and
 attribute names will be defined in a future
 standards-track revision to [DISPOSITION].
 body language
 A string or parenthesized list giving the body
 language value as defined in [LANGUAGE-TAGS].
 Any following extension data are not yet defined in
 this version of the protocol. Such extension data
 can consist of zero or more NILs, strings, numbers,
 or potentially nested parenthesized lists of such
 data. Client implementations that do a
 BODYSTRUCTURE fetch MUST be prepared to accept such
 extension data. Server implementations MUST NOT
 send such extension data until it has been defined
 by a revision of this protocol.
 The basic fields of a non-multipart body part are
 in the following order:
 body type
 A string giving the content media type name as
 defined in [MIME-IMB].
 body subtype
 A string giving the content subtype name as
 defined in [MIME-IMB].
 body parameter parenthesized list
 A parenthesized list of attribute/value pairs
 [e.g. ("foo" "bar" "baz" "rag") where "bar" is
 the value of "foo" and "rag" is the value of
 "baz"] as defined in [MIME-IMB].
 body id
 A string giving the content id as defined in
 [MIME-IMB].
 body description
 A string giving the content description as
 defined in [MIME-IMB].
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RFC 2060 IMAP4rev1 December 1996
 body encoding
 A string giving the content transfer encoding as
 defined in [MIME-IMB].
 body size
 A number giving the size of the body in octets.
 Note that this size is the size in its transfer
 encoding and not the resulting size after any
 decoding.
 A body type of type MESSAGE and subtype RFC822
 contains, immediately after the basic fields, the
 envelope structure, body structure, and size in
 text lines of the encapsulated message.
 A body type of type TEXT contains, immediately
 after the basic fields, the size of the body in
 text lines. Note that this size is the size in its
 content transfer encoding and not the resulting
 size after any decoding.
 Extension data follows the basic fields and the
 type-specific fields listed above. Extension data
 is never returned with the BODY fetch, but can be
 returned with a BODYSTRUCTURE fetch. Extension
 data, if present, MUST be in the defined order.
 The extension data of a non-multipart body part are
 in the following order:
 body MD5
 A string giving the body MD5 value as defined in
 [MD5].
 body disposition
 A parenthesized list with the same content and
 function as the body disposition for a multipart
 body part.
 body language
 A string or parenthesized list giving the body
 language value as defined in [LANGUAGE-TAGS].
 Any following extension data are not yet defined in
 this version of the protocol, and would be as
 described above under multipart extension data.
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RFC 2060 IMAP4rev1 December 1996
 ENVELOPE A parenthesized list that describes the envelope
 structure of a message. This is computed by the
 server by parsing the [RFC-822] header into the
 component parts, defaulting various fields as
 necessary.
 The fields of the envelope structure are in the
 following order: date, subject, from, sender,
 reply-to, to, cc, bcc, in-reply-to, and message-id.
 The date, subject, in-reply-to, and message-id
 fields are strings. The from, sender, reply-to,
 to, cc, and bcc fields are parenthesized lists of
 address structures.
 An address structure is a parenthesized list that
 describes an electronic mail address. The fields
 of an address structure are in the following order:
 personal name, [SMTP] at-domain-list (source
 route), mailbox name, and host name.
 [RFC-822] group syntax is indicated by a special
 form of address structure in which the host name
 field is NIL. If the mailbox name field is also
 NIL, this is an end of group marker (semi-colon in
 RFC 822 syntax). If the mailbox name field is
 non-NIL, this is a start of group marker, and the
 mailbox name field holds the group name phrase.
 Any field of an envelope or address structure that
 is not applicable is presented as NIL. Note that
 the server MUST default the reply-to and sender
 fields from the from field; a client is not
 expected to know to do this.
 FLAGS A parenthesized list of flags that are set for this
 message.
 INTERNALDATE A string representing the internal date of the
 message.
 RFC822 Equivalent to BODY[].
 RFC822.HEADER Equivalent to BODY.PEEK[HEADER].
 RFC822.SIZE A number expressing the [RFC-822] size of the
 message.
 RFC822.TEXT Equivalent to BODY[TEXT].
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RFC 2060 IMAP4rev1 December 1996
 UID A number expressing the unique identifier of the
 message.
 Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)
7.5. Server Responses - Command Continuation Request
 The command continuation request response is indicated by a "+" token
 instead of a tag. This form of response indicates that the server is
 ready to accept the continuation of a command from the client. The
 remainder of this response is a line of text.
 This response is used in the AUTHORIZATION command to transmit server
 data to the client, and request additional client data. This
 response is also used if an argument to any command is a literal.
 The client is not permitted to send the octets of the literal unless
 the server indicates that it expects it. This permits the server to
 process commands and reject errors on a line-by-line basis. The
 remainder of the command, including the CRLF that terminates a
 command, follows the octets of the literal. If there are any
 additional command arguments the literal octets are followed by a
 space and those arguments.
 Example: C: A001 LOGIN {11}
 S: + Ready for additional command text
 C: FRED FOOBAR {7}
 S: + Ready for additional command text
 C: fat man
 S: A001 OK LOGIN completed
 C: A044 BLURDYBLOOP {102856}
 S: A044 BAD No such command as "BLURDYBLOOP"
. Sample IMAP4rev1 connection
 The following is a transcript of an IMAP4rev1 connection. A long
 line in this sample is broken for editorial clarity.
S: * OK IMAP4rev1 Service Ready
C: a001 login mrc secret
S: a001 OK LOGIN completed
C: a002 select inbox
S: * 18 EXISTS
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * 2 RECENT
S: * OK [UNSEEN 17] Message 17 is the first unseen message
S: * OK [UIDVALIDITY 3857529045] UIDs valid
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RFC 2060 IMAP4rev1 December 1996
S: a002 OK [READ-WRITE] SELECT completed
C: a003 fetch 12 full
S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "17-Jul-1996 02:44:25 -0700"
 RFC822.SIZE 4286 ENVELOPE ("1996年7月17日 02:23:25 -0700 (PDT)"
 "IMAP4rev1 WG mtg summary and minutes"
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 (("Terry Gray" NIL "gray" "cac.washington.edu"))
 ((NIL NIL "imap" "cac.washington.edu"))
 ((NIL NIL "minutes" "CNRI.Reston.VA.US")
 ("John Klensin" NIL "KLENSIN" "INFOODS.MIT.EDU")) NIL NIL
 "<B27397-0100000@cac.washington.edu>")
 BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 3028 92))
S: a003 OK FETCH completed
C: a004 fetch 12 body[header]
S: * 12 FETCH (BODY[HEADER] {350}
S: Date: 1996年7月17日 02:23:25 -0700 (PDT)
S: From: Terry Gray <gray@cac.washington.edu>
S: Subject: IMAP4rev1 WG mtg summary and minutes
S: To: imap@cac.washington.edu
S: cc: minutes@CNRI.Reston.VA.US, John Klensin <KLENSIN@INFOODS.MIT.EDU>
S: Message-Id: <B27397-0100000@cac.washington.edu>
S: MIME-Version: 1.0
S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
S:
S: )
S: a004 OK FETCH completed
C: a005 store 12 +flags \deleted
S: * 12 FETCH (FLAGS (\Seen \Deleted))
S: a005 OK +FLAGS completed
C: a006 logout
S: * BYE IMAP4rev1 server terminating connection
S: a006 OK LOGOUT completed
. Formal Syntax
 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) notation as specified in [RFC-822] with one exception; the
 delimiter used with the "#" construct is a single space (SPACE) and
 not one or more commas.
 In the case of alternative or optional rules in which a later rule
 overlaps an earlier rule, the rule which is listed earlier MUST take
 priority. For example, "\Seen" when parsed as a flag is the \Seen
 flag name and not a flag_extension, even though "\Seen" could be
 parsed as a flag_extension. Some, but not all, instances of this
 rule are noted below.
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RFC 2060 IMAP4rev1 December 1996
 Except as noted otherwise, all alphabetic characters are case-
 insensitive. The use of upper or lower case characters to define
 token strings is for editorial clarity only. Implementations MUST
 accept these strings in a case-insensitive fashion.
address ::= "(" addr_name SPACE addr_adl SPACE addr_mailbox
 SPACE addr_host ")"
addr_adl ::= nstring
 ;; Holds route from [RFC-822] route-addr if
 ;; non-NIL
addr_host ::= nstring
 ;; NIL indicates [RFC-822] group syntax.
 ;; Otherwise, holds [RFC-822] domain name
addr_mailbox ::= nstring
 ;; NIL indicates end of [RFC-822] group; if
 ;; non-NIL and addr_host is NIL, holds
 ;; [RFC-822] group name.
 ;; Otherwise, holds [RFC-822] local-part
addr_name ::= nstring
 ;; Holds phrase from [RFC-822] mailbox if
 ;; non-NIL
alpha ::= "A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" /
 "I" / "J" / "K" / "L" / "M" / "N" / "O" / "P" /
 "Q" / "R" / "S" / "T" / "U" / "V" / "W" / "X" /
 "Y" / "Z" /
 "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" /
 "i" / "j" / "k" / "l" / "m" / "n" / "o" / "p" /
 "q" / "r" / "s" / "t" / "u" / "v" / "w" / "x" /
 "y" / "z"
 ;; Case-sensitive
append ::= "APPEND" SPACE mailbox [SPACE flag_list]
 [SPACE date_time] SPACE literal
astring ::= atom / string
atom ::= 1*ATOM_CHAR
ATOM_CHAR ::= <any CHAR except atom_specials>
atom_specials ::= "(" / ")" / "{" / SPACE / CTL / list_wildcards /
 quoted_specials
Crispin Standards Track [Page 65]

---

RFC 2060 IMAP4rev1 December 1996
authenticate ::= "AUTHENTICATE" SPACE auth_type *(CRLF base64)
auth_type ::= atom
 ;; Defined by [IMAP-AUTH]
base64 ::= *(4base64_char) [base64_terminal]
base64_char ::= alpha / digit / "+" / "/"
base64_terminal ::= (2base64_char "==") / (3base64_char "=")
body ::= "(" body_type_1part / body_type_mpart ")"
body_extension ::= nstring / number / "(" 1#body_extension ")"
 ;; Future expansion. Client implementations
 ;; MUST accept body_extension fields. Server
 ;; implementations MUST NOT generate
 ;; body_extension fields except as defined by
 ;; future standard or standards-track
 ;; revisions of this specification.
body_ext_1part ::= body_fld_md5 [SPACE body_fld_dsp
 [SPACE body_fld_lang
 [SPACE 1#body_extension]]]
 ;; MUST NOT be returned on non-extensible
 ;; "BODY" fetch
body_ext_mpart ::= body_fld_param
 [SPACE body_fld_dsp SPACE body_fld_lang
 [SPACE 1#body_extension]]
 ;; MUST NOT be returned on non-extensible
 ;; "BODY" fetch
body_fields ::= body_fld_param SPACE body_fld_id SPACE
 body_fld_desc SPACE body_fld_enc SPACE
 body_fld_octets
body_fld_desc ::= nstring
body_fld_dsp ::= "(" string SPACE body_fld_param ")" / nil
body_fld_enc ::= (<"> ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
 "QUOTED-PRINTABLE") <">) / string
body_fld_id ::= nstring
body_fld_lang ::= nstring / "(" 1#string ")"
Crispin Standards Track [Page 66]

---

RFC 2060 IMAP4rev1 December 1996
body_fld_lines ::= number
body_fld_md5 ::= nstring
body_fld_octets ::= number
body_fld_param ::= "(" 1#(string SPACE string) ")" / nil
body_type_1part ::= (body_type_basic / body_type_msg / body_type_text)
 [SPACE body_ext_1part]
body_type_basic ::= media_basic SPACE body_fields
 ;; MESSAGE subtype MUST NOT be "RFC822"
body_type_mpart ::= 1*body SPACE media_subtype
 [SPACE body_ext_mpart]
body_type_msg ::= media_message SPACE body_fields SPACE envelope
 SPACE body SPACE body_fld_lines
body_type_text ::= media_text SPACE body_fields SPACE body_fld_lines
capability ::= "AUTH=" auth_type / atom
 ;; New capabilities MUST begin with "X" or be
 ;; registered with IANA as standard or
 ;; standards-track
capability_data ::= "CAPABILITY" SPACE [1#capability SPACE] "IMAP4rev1"
 [SPACE 1#capability]
 ;; IMAP4rev1 servers which offer RFC 1730
 ;; compatibility MUST list "IMAP4" as the first
 ;; capability.
CHAR ::= <any 7-bit US-ASCII character except NUL,
 0x01 - 0x7f>
CHAR8 ::= <any 8-bit octet except NUL, 0x01 - 0xff>
command ::= tag SPACE (command_any / command_auth /
 command_nonauth / command_select) CRLF
 ;; Modal based on state
command_any ::= "CAPABILITY" / "LOGOUT" / "NOOP" / x_command
 ;; Valid in all states
command_auth ::= append / create / delete / examine / list / lsub /
 rename / select / status / subscribe / unsubscribe
 ;; Valid only in Authenticated or Selected state
Crispin Standards Track [Page 67]

---

RFC 2060 IMAP4rev1 December 1996
command_nonauth ::= login / authenticate
 ;; Valid only when in Non-Authenticated state
command_select ::= "CHECK" / "CLOSE" / "EXPUNGE" /
 copy / fetch / store / uid / search
 ;; Valid only when in Selected state
continue_req ::= "+" SPACE (resp_text / base64)
copy ::= "COPY" SPACE set SPACE mailbox
CR ::= <ASCII CR, carriage return, 0x0D>
create ::= "CREATE" SPACE mailbox
 ;; Use of INBOX gives a NO error
CRLF ::= CR LF
CTL ::= <any ASCII control character and DEL,
 0x00 - 0x1f, 0x7f>
date ::= date_text / <"> date_text <">
date_day ::= 1*2digit
 ;; Day of month
date_day_fixed ::= (SPACE digit) / 2digit
 ;; Fixed-format version of date_day
date_month ::= "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" /
 "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"
date_text ::= date_day "-" date_month "-" date_year
date_year ::= 4digit
date_time ::= <"> date_day_fixed "-" date_month "-" date_year
 SPACE time SPACE zone <">
delete ::= "DELETE" SPACE mailbox
 ;; Use of INBOX gives a NO error
digit ::= "0" / digit_nz
digit_nz ::= "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" /
 "9"
Crispin Standards Track [Page 68]

---

RFC 2060 IMAP4rev1 December 1996
envelope ::= "(" env_date SPACE env_subject SPACE env_from
 SPACE env_sender SPACE env_reply_to SPACE env_to
 SPACE env_cc SPACE env_bcc SPACE env_in_reply_to
 SPACE env_message_id ")"
env_bcc ::= "(" 1*address ")" / nil
env_cc ::= "(" 1*address ")" / nil
env_date ::= nstring
env_from ::= "(" 1*address ")" / nil
env_in_reply_to ::= nstring
env_message_id ::= nstring
env_reply_to ::= "(" 1*address ")" / nil
env_sender ::= "(" 1*address ")" / nil
env_subject ::= nstring
env_to ::= "(" 1*address ")" / nil
examine ::= "EXAMINE" SPACE mailbox
fetch ::= "FETCH" SPACE set SPACE ("ALL" / "FULL" /
 "FAST" / fetch_att / "(" 1#fetch_att ")")
fetch_att ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" /
 "RFC822" [".HEADER" / ".SIZE" / ".TEXT"] /
 "BODY" ["STRUCTURE"] / "UID" /
 "BODY" [".PEEK"] section
 ["<" number "." nz_number ">"]
flag ::= "\Answered" / "\Flagged" / "\Deleted" /
 "\Seen" / "\Draft" / flag_keyword / flag_extension
flag_extension ::= "\" atom
 ;; Future expansion. Client implementations
 ;; MUST accept flag_extension flags. Server
 ;; implementations MUST NOT generate
 ;; flag_extension flags except as defined by
 ;; future standard or standards-track
 ;; revisions of this specification.
flag_keyword ::= atom
Crispin Standards Track [Page 69]

---

RFC 2060 IMAP4rev1 December 1996
flag_list ::= "(" #flag ")"
greeting ::= "*" SPACE (resp_cond_auth / resp_cond_bye) CRLF
header_fld_name ::= astring
header_list ::= "(" 1#header_fld_name ")"
LF ::= <ASCII LF, line feed, 0x0A>
list ::= "LIST" SPACE mailbox SPACE list_mailbox
list_mailbox ::= 1*(ATOM_CHAR / list_wildcards) / string
list_wildcards ::= "%" / "*"
literal ::= "{" number "}" CRLF *CHAR8
 ;; Number represents the number of CHAR8 octets
login ::= "LOGIN" SPACE userid SPACE password
lsub ::= "LSUB" SPACE mailbox SPACE list_mailbox
mailbox ::= "INBOX" / astring
 ;; INBOX is case-insensitive. All case variants of
 ;; INBOX (e.g. "iNbOx") MUST be interpreted as INBOX
 ;; not as an astring. Refer to section 5.1 for
 ;; further semantic details of mailbox names.
mailbox_data ::= "FLAGS" SPACE flag_list /
 "LIST" SPACE mailbox_list /
 "LSUB" SPACE mailbox_list /
 "MAILBOX" SPACE text /
 "SEARCH" [SPACE 1#nz_number] /
 "STATUS" SPACE mailbox SPACE
 "(" #<status_att number ")" /
 number SPACE "EXISTS" / number SPACE "RECENT"
mailbox_list ::= "(" #("\Marked" / "\Noinferiors" /
 "\Noselect" / "\Unmarked" / flag_extension) ")"
 SPACE (<"> QUOTED_CHAR <"> / nil) SPACE mailbox
media_basic ::= (<"> ("APPLICATION" / "AUDIO" / "IMAGE" /
 "MESSAGE" / "VIDEO") <">) / string)
 SPACE media_subtype
 ;; Defined in [MIME-IMT]
media_message ::= <"> "MESSAGE" <"> SPACE <"> "RFC822" <">
Crispin Standards Track [Page 70]

---

RFC 2060 IMAP4rev1 December 1996
 ;; Defined in [MIME-IMT]
media_subtype ::= string
 ;; Defined in [MIME-IMT]
media_text ::= <"> "TEXT" <"> SPACE media_subtype
 ;; Defined in [MIME-IMT]
message_data ::= nz_number SPACE ("EXPUNGE" /
 ("FETCH" SPACE msg_att))
msg_att ::= "(" 1#("ENVELOPE" SPACE envelope /
 "FLAGS" SPACE "(" #(flag / "\Recent") ")" /
 "INTERNALDATE" SPACE date_time /
 "RFC822" [".HEADER" / ".TEXT"] SPACE nstring /
 "RFC822.SIZE" SPACE number /
 "BODY" ["STRUCTURE"] SPACE body /
 "BODY" section ["<" number ">"] SPACE nstring /
 "UID" SPACE uniqueid) ")"
nil ::= "NIL"
nstring ::= string / nil
number ::= 1*digit
 ;; Unsigned 32-bit integer
 ;; (0 <= n < 4,294,967,296)
nz_number ::= digit_nz *digit
 ;; Non-zero unsigned 32-bit integer
 ;; (0 < n < 4,294,967,296)
password ::= astring
quoted ::= <"> *QUOTED_CHAR <">
QUOTED_CHAR ::= <any TEXT_CHAR except quoted_specials> /
 "\" quoted_specials
quoted_specials ::= <"> / "\"
rename ::= "RENAME" SPACE mailbox SPACE mailbox
 ;; Use of INBOX as a destination gives a NO error
response ::= *(continue_req / response_data) response_done
response_data ::= "*" SPACE (resp_cond_state / resp_cond_bye /
 mailbox_data / message_data / capability_data)
Crispin Standards Track [Page 71]

---

RFC 2060 IMAP4rev1 December 1996
 CRLF
response_done ::= response_tagged / response_fatal
response_fatal ::= "*" SPACE resp_cond_bye CRLF
 ;; Server closes connection immediately
response_tagged ::= tag SPACE resp_cond_state CRLF
resp_cond_auth ::= ("OK" / "PREAUTH") SPACE resp_text
 ;; Authentication condition
resp_cond_bye ::= "BYE" SPACE resp_text
resp_cond_state ::= ("OK" / "NO" / "BAD") SPACE resp_text
 ;; Status condition
resp_text ::= ["[" resp_text_code "]" SPACE] (text_mime2 / text)
 ;; text SHOULD NOT begin with "[" or "="
resp_text_code ::= "ALERT" / "PARSE" /
 "PERMANENTFLAGS" SPACE "(" #(flag / "\*") ")" /
 "READ-ONLY" / "READ-WRITE" / "TRYCREATE" /
 "UIDVALIDITY" SPACE nz_number /
 "UNSEEN" SPACE nz_number /
 atom [SPACE 1*<any TEXT_CHAR except "]">]
search ::= "SEARCH" SPACE ["CHARSET" SPACE astring SPACE]
 1#search_key
 ;; [CHARSET] MUST be registered with IANA
search_key ::= "ALL" / "ANSWERED" / "BCC" SPACE astring /
 "BEFORE" SPACE date / "BODY" SPACE astring /
 "CC" SPACE astring / "DELETED" / "FLAGGED" /
 "FROM" SPACE astring /
 "KEYWORD" SPACE flag_keyword / "NEW" / "OLD" /
 "ON" SPACE date / "RECENT" / "SEEN" /
 "SINCE" SPACE date / "SUBJECT" SPACE astring /
 "TEXT" SPACE astring / "TO" SPACE astring /
 "UNANSWERED" / "UNDELETED" / "UNFLAGGED" /
 "UNKEYWORD" SPACE flag_keyword / "UNSEEN" /
 ;; Above this line were in [IMAP2]
 "DRAFT" /
 "HEADER" SPACE header_fld_name SPACE astring /
 "LARGER" SPACE number / "NOT" SPACE search_key /
 "OR" SPACE search_key SPACE search_key /
 "SENTBEFORE" SPACE date / "SENTON" SPACE date /
 "SENTSINCE" SPACE date / "SMALLER" SPACE number /
Crispin Standards Track [Page 72]

---

RFC 2060 IMAP4rev1 December 1996
 "UID" SPACE set / "UNDRAFT" / set /
 "(" 1#search_key ")"
section ::= "[" [section_text / (nz_number *["." nz_number]
 ["." (section_text / "MIME")])] "]"
section_text ::= "HEADER" / "HEADER.FIELDS" [".NOT"]
 SPACE header_list / "TEXT"
select ::= "SELECT" SPACE mailbox
sequence_num ::= nz_number / "*"
 ;; * is the largest number in use. For message
 ;; sequence numbers, it is the number of messages
 ;; in the mailbox. For unique identifiers, it is
 ;; the unique identifier of the last message in
 ;; the mailbox.
set ::= sequence_num / (sequence_num ":" sequence_num) /
 (set "," set)
 ;; Identifies a set of messages. For message
 ;; sequence numbers, these are consecutive
 ;; numbers from 1 to the number of messages in
 ;; the mailbox
 ;; Comma delimits individual numbers, colon
 ;; delimits between two numbers inclusive.
 ;; Example: 2,4:7,9,12:* is 2,4,5,6,7,9,12,13,
 ;; 14,15 for a mailbox with 15 messages.
SPACE ::= <ASCII SP, space, 0x20>
status ::= "STATUS" SPACE mailbox SPACE "(" 1#status_att ")"
status_att ::= "MESSAGES" / "RECENT" / "UIDNEXT" / "UIDVALIDITY" /
 "UNSEEN"
store ::= "STORE" SPACE set SPACE store_att_flags
store_att_flags ::= (["+" / "-"] "FLAGS" [".SILENT"]) SPACE
 (flag_list / #flag)
string ::= quoted / literal
subscribe ::= "SUBSCRIBE" SPACE mailbox
tag ::= 1*<any ATOM_CHAR except "+">
text ::= 1*TEXT_CHAR
Crispin Standards Track [Page 73]

---

RFC 2060 IMAP4rev1 December 1996
text_mime2 ::= "=?" <charset> "?" <encoding> "?"
 <encoded-text> "?="
 ;; Syntax defined in [MIME-HDRS]
TEXT_CHAR ::= <any CHAR except CR and LF>
time ::= 2digit ":" 2digit ":" 2digit
 ;; Hours minutes seconds
uid ::= "UID" SPACE (copy / fetch / search / store)
 ;; Unique identifiers used instead of message
 ;; sequence numbers
uniqueid ::= nz_number
 ;; Strictly ascending
unsubscribe ::= "UNSUBSCRIBE" SPACE mailbox
userid ::= astring
x_command ::= "X" atom <experimental command arguments>
zone ::= ("+" / "-") 4digit
 ;; Signed four-digit value of hhmm representing
 ;; hours and minutes west of Greenwich (that is,
 ;; (the amount that the given time differs from
 ;; Universal Time). Subtracting the timezone
 ;; from the given time will give the UT form.
 ;; The Universal Time zone is "+0000".
. Author's Note
 This document is a revision or rewrite of earlier documents, and
 supercedes the protocol specification in those documents: RFC 1730,
 unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.
. Security Considerations
 IMAP4rev1 protocol transactions, including electronic mail data, are
 sent in the clear over the network unless privacy protection is
 negotiated in the AUTHENTICATE command.
 A server error message for an AUTHENTICATE command which fails due to
 invalid credentials SHOULD NOT detail why the credentials are
 invalid.
 Use of the LOGIN command sends passwords in the clear. This can be
 avoided by using the AUTHENTICATE command instead.
Crispin Standards Track [Page 74]

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RFC 2060 IMAP4rev1 December 1996
 A server error message for a failing LOGIN command SHOULD NOT specify
 that the user name, as opposed to the password, is invalid.
 Additional security considerations are discussed in the section
 discussing the AUTHENTICATE and LOGIN commands.
. Author's Address
 Mark R. Crispin
 Networks and Distributed Computing
 University of Washington
 4545 15th Aveneue NE
 Seattle, WA 98105-4527
 Phone: (206) 543-5762
 EMail: MRC@CAC.Washington.EDU
Crispin Standards Track [Page 75]

---

RFC 2060 IMAP4rev1 December 1996
Appendices
A. References
[ACAP] Myers, J. "ACAP -- Application Configuration Access Protocol",
Work in Progress.
[CHARSET] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
RFC 1700, USC/Information Sciences Institute, October 1994.
[DISPOSITION] Troost, R., and Dorner, S., "Communicating Presentation
Information in Internet Messages: The Content-Disposition Header",
RFC 1806, June 1995.
[IMAP-AUTH] Myers, J., "IMAP4 Authentication Mechanism", RFC 1731.
Carnegie-Mellon University, December 1994.
[IMAP-COMPAT] Crispin, M., "IMAP4 Compatibility with IMAP2bis", RFC
2061, University of Washington, November 1996.
[IMAP-DISC] Austein, R., "Synchronization Operations for Disconnected
IMAP4 Clients", Work in Progress.
[IMAP-HISTORICAL] Crispin, M. "IMAP4 Compatibility with IMAP2 and
IMAP2bis", RFC 1732, University of Washington, December 1994.
[IMAP-MODEL] Crispin, M., "Distributed Electronic Mail Models in
IMAP4", RFC 1733, University of Washington, December 1994.
[IMAP-OBSOLETE] Crispin, M., "Internet Message Access Protocol -
Obsolete Syntax", RFC 2062, University of Washington, November 1996.
[IMAP2] Crispin, M., "Interactive Mail Access Protocol - Version 2",
RFC 1176, University of Washington, August 1990.
[LANGUAGE-TAGS] Alvestrand, H., "Tags for the Identification of
Languages", RFC 1766, March 1995.
[MD5] Myers, J., and M. Rose, "The Content-MD5 Header Field", RFC
1864, October 1995.
[MIME-IMB] Freed, N., and N. Borenstein, "MIME (Multipurpose Internet
Mail Extensions) Part One: Format of Internet Message Bodies", RFC
2045, November 1996.
[MIME-IMT] Freed, N., and N. Borenstein, "MIME (Multipurpose
Internet Mail Extensions) Part Two: Media Types", RFC 2046,
November 1996.
Crispin Standards Track [Page 76]

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RFC 2060 IMAP4rev1 December 1996
[MIME-HDRS] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text", RFC
2047, November 1996.
[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, University of Delaware, August 1982.
[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, USC/Information Sciences Institute, August 1982.
[UTF-7] Goldsmith, D., and Davis, M., "UTF-7: A Mail-Safe
Transformation Format of Unicode", RFC 1642, July 1994.
B. Changes from RFC 1730 
1) The STATUS command has been added.
2) Clarify in the formal syntax that the "#" construct can never
refer to multiple spaces.
3) Obsolete syntax has been moved to a separate document.
4) The PARTIAL command has been obsoleted.
5) The RFC822.HEADER.LINES, RFC822.HEADER.LINES.NOT, RFC822.PEEK, and
RFC822.TEXT.PEEK fetch attributes have been obsoleted.
6) The "<" origin "." size ">" suffix for BODY text attributes has
been added.
7) The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, MIME, and TEXT part
specifiers have been added.
8) Support for Content-Disposition and Content-Language has been
added.
9) The restriction on fetching nested MULTIPART parts has been
removed.
10) Body part number 0 has been obsoleted.
11) Server-supported authenticators are now identified by
capabilities.
Crispin Standards Track [Page 77]

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RFC 2060 IMAP4rev1 December 1996
12) The capability that identifies this protocol is now called
"IMAP4rev1". A server that provides backwards support for RFC 1730
SHOULD emit the "IMAP4" capability in addition to "IMAP4rev1" in its
CAPABILITY response. Because RFC-1730 required "IMAP4" to appear as
the first capability, it MUST listed first in the response.
13) A description of the mailbox name namespace convention has been
added.
14) A description of the international mailbox name convention has
been added.
15) The UID-NEXT and UID-VALIDITY status items are now called UIDNEXT
and UIDVALIDITY. This is a change from the IMAP STATUS
Work in Progress and not from RFC-1730
16) Add a clarification that a null mailbox name argument to the LIST
command returns an untagged LIST response with the hierarchy
delimiter and root of the reference argument.
17) Define terms such as "MUST", "SHOULD", and "MUST NOT".
18) Add a section which defines message attributes and more
thoroughly details the semantics of message sequence numbers, UIDs,
and flags.
19) Add a clarification detailing the circumstances when a client may
send multiple commands without waiting for a response, and the
circumstances in which ambiguities may result.
20) Add a recommendation on server behavior for DELETE and RENAME
when inferior hierarchical names of the given name exist.
21) Add a clarification that a mailbox name may not be unilaterally
unsubscribed by the server, even if that mailbox name no longer
exists.
22) Add a clarification that LIST should return its results quickly
without undue delay.
23) Add a clarification that the date_time argument to APPEND sets
the internal date of the message.
24) Add a clarification on APPEND behavior when the target mailbox is
the currently selected mailbox.
Crispin Standards Track [Page 78]

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RFC 2060 IMAP4rev1 December 1996
25) Add a clarification that external changes to flags should be
always announced via an untagged FETCH even if the current command is
a STORE with the ".SILENT" suffix.
26) Add a clarification that COPY appends to the target mailbox.
27) Add the NEWNAME response code.
28) Rewrite the description of the untagged BYE response to clarify
its semantics.
29) Change the reference for the body MD5 to refer to the proper RFC.
30) Clarify that the formal syntax contains rules which may overlap,
and that in the event of such an overlap the rule which occurs first
takes precedence.
31) Correct the definition of body_fld_param.
32) More formal syntax for capability_data.
33) Clarify that any case variant of "INBOX" must be interpreted as
INBOX.
34) Clarify that the human-readable text in resp_text should not
begin with "[" or "=".
35) Change MIME references to Draft Standard documents.
36) Clarify \Recent semantics.
37) Additional examples.
C. Key Word Index
 +FLAGS <flag list> (store command data item) ............... 45
 +FLAGS.SILENT <flag list> (store command data item) ........ 46
 -FLAGS <flag list> (store command data item) ............... 46
 -FLAGS.SILENT <flag list> (store command data item) ........ 46
 ALERT (response code) ...................................... 50
 ALL (fetch item) ........................................... 41
 ALL (search key) ........................................... 38
 ANSWERED (search key) ...................................... 38
 APPEND (command) ........................................... 34
 AUTHENTICATE (command) ..................................... 20
 BAD (response) ............................................. 52
 BCC <string> (search key) .................................. 38
 BEFORE <date> (search key) ................................. 39
Crispin Standards Track [Page 79]

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RFC 2060 IMAP4rev1 December 1996
 BODY (fetch item) .......................................... 41
 BODY (fetch result) ........................................ 58
 BODY <string> (search key) ................................. 39
 BODY.PEEK[<section>]<<partial>> (fetch item) ............... 44
 BODYSTRUCTURE (fetch item) ................................. 44
 BODYSTRUCTURE (fetch result) ............................... 59
 BODY[<section>]<<origin_octet>> (fetch result) ............. 58
 BODY[<section>]<<partial>> (fetch item) .................... 41
 BYE (response) ............................................. 52
 Body Structure (message attribute) ......................... 11
 CAPABILITY (command) ....................................... 18
 CAPABILITY (response) ...................................... 53
 CC <string> (search key) ................................... 39
 CHECK (command) ............................................ 36
 CLOSE (command) ............................................ 36
 COPY (command) ............................................. 46
 CREATE (command) ........................................... 25
 DELETE (command) ........................................... 26
 DELETED (search key) ....................................... 39
 DRAFT (search key) ......................................... 39
 ENVELOPE (fetch item) ...................................... 44
 ENVELOPE (fetch result) .................................... 62
 EXAMINE (command) .......................................... 24
 EXISTS (response) .......................................... 56
 EXPUNGE (command) .......................................... 37
 EXPUNGE (response) ......................................... 57
 Envelope Structure (message attribute) ..................... 11
 FAST (fetch item) .......................................... 44
 FETCH (command) ............................................ 41
 FETCH (response) ........................................... 58
 FLAGGED (search key) ....................................... 39
 FLAGS (fetch item) ......................................... 44
 FLAGS (fetch result) ....................................... 62
 FLAGS (response) ........................................... 56
 FLAGS <flag list> (store command data item) ................ 45
 FLAGS.SILENT <flag list> (store command data item) ......... 45
 FROM <string> (search key) ................................. 39
 FULL (fetch item) .......................................... 44
 Flags (message attribute) .................................. 9
 HEADER (part specifier) .................................... 41
 HEADER <field-name> <string> (search key) .................. 39
 HEADER.FIELDS <header_list> (part specifier) ............... 41
 HEADER.FIELDS.NOT <header_list> (part specifier) ........... 41
 INTERNALDATE (fetch item) .................................. 44
 INTERNALDATE (fetch result) ................................ 62
 Internal Date (message attribute) .......................... 10
 KEYWORD <flag> (search key) ................................ 39
 Keyword (type of flag) ..................................... 10
Crispin Standards Track [Page 80]

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RFC 2060 IMAP4rev1 December 1996
 LARGER <n> (search key) .................................... 39
 LIST (command) ............................................. 30
 LIST (response) ............................................ 54
 LOGIN (command) ............................................ 22
 LOGOUT (command) ........................................... 20
 LSUB (command) ............................................. 32
 LSUB (response) ............................................ 55
 MAY (specification requirement term) ....................... 5
 MESSAGES (status item) ..................................... 33
 MIME (part specifier) ...................................... 42
 MUST (specification requirement term) ...................... 4
 MUST NOT (specification requirement term) .................. 4
 Message Sequence Number (message attribute) ................ 9
 NEW (search key) ........................................... 39
 NEWNAME (response code) .................................... 50
 NO (response) .............................................. 51
 NOOP (command) ............................................. 19
 NOT <search-key> (search key) .............................. 39
 OK (response) .............................................. 51
 OLD (search key) ........................................... 39
 ON <date> (search key) ..................................... 39
 OPTIONAL (specification requirement term) .................. 5
 OR <search-key1> <search-key2> (search key) ................ 39
 PARSE (response code) ...................................... 50
 PERMANENTFLAGS (response code) ............................. 50
 PREAUTH (response) ......................................... 52
 Permanent Flag (class of flag) ............................. 10
 READ-ONLY (response code) .................................. 50
 READ-WRITE (response code) ................................. 50
 RECENT (response) .......................................... 57
 RECENT (search key) ........................................ 39
 RECENT (status item) ....................................... 33
 RENAME (command) ........................................... 27
 REQUIRED (specification requirement term) .................. 4
 RFC822 (fetch item) ........................................ 44
 RFC822 (fetch result) ...................................... 63
 RFC822.HEADER (fetch item) ................................. 44
 RFC822.HEADER (fetch result) ............................... 62
 RFC822.SIZE (fetch item) ................................... 44
 RFC822.SIZE (fetch result) ................................. 62
 RFC822.TEXT (fetch item) ................................... 44
 RFC822.TEXT (fetch result) ................................. 62
 SEARCH (command) ........................................... 37
 SEARCH (response) .......................................... 55
 SEEN (search key) .......................................... 40
 SELECT (command) ........................................... 23
 SENTBEFORE <date> (search key) ............................. 40
 SENTON <date> (search key) ................................. 40
Crispin Standards Track [Page 81]

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RFC 2060 IMAP4rev1 December 1996
 SENTSINCE <date> (search key) .............................. 40
 SHOULD (specification requirement term) .................... 5
 SHOULD NOT (specification requirement term) ................ 5
 SINCE <date> (search key) .................................. 40
 SMALLER <n> (search key) ................................... 40
 STATUS (command) ........................................... 33
 STATUS (response) .......................................... 55
 STORE (command) ............................................ 45
 SUBJECT <string> (search key) .............................. 40
 SUBSCRIBE (command) ........................................ 29
 Session Flag (class of flag) ............................... 10
 System Flag (type of flag) ................................. 9
 TEXT (part specifier) ...................................... 42
 TEXT <string> (search key) ................................. 40
 TO <string> (search key) ................................... 40
 TRYCREATE (response code) .................................. 51
 UID (command) .............................................. 47
 UID (fetch item) ........................................... 44
 UID (fetch result) ......................................... 63
 UID <message set> (search key) ............................. 40
 UIDNEXT (status item) ...................................... 33
 UIDVALIDITY (response code) ................................ 51
 UIDVALIDITY (status item) .................................. 34
 UNANSWERED (search key) .................................... 40
 UNDELETED (search key) ..................................... 40
 UNDRAFT (search key) ....................................... 40
 UNFLAGGED (search key) ..................................... 40
 UNKEYWORD <flag> (search key) .............................. 40
 UNSEEN (response code) ..................................... 51
 UNSEEN (search key) ........................................ 40
 UNSEEN (status item) ....................................... 34
 UNSUBSCRIBE (command) ...................................... 30
 Unique Identifier (UID) (message attribute) ................ 7
 X<atom> (command) .......................................... 48
 [RFC-822] Size (message attribute) ......................... 11
 \Answered (system flag) .................................... 9
 \Deleted (system flag) ..................................... 9
 \Draft (system flag) ....................................... 9
 \Flagged (system flag) ..................................... 9
 \Marked (mailbox name attribute) ........................... 54
 \Noinferiors (mailbox name attribute) ...................... 54
 \Noselect (mailbox name attribute) ......................... 54
 \Recent (system flag) ...................................... 10
 \Seen (system flag) ........................................ 9
 \Unmarked (mailbox name attribute) ......................... 54
Crispin Standards Track [Page 82]

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