RFC # 822
 Obsoletes: RFC #733 (NIC #41952)
 STANDARD FOR THE FORMAT OF
 ARPA INTERNET TEXT MESSAGES
 August 13, 1982
 Revised by
 David H. Crocker
 Dept. of Electrical Engineering
 University of Delaware, Newark, DE 19711
 Network: DCrocker @ UDel-Relay
 Standard for ARPA Internet Text Messages
 TABLE OF CONTENTS
 PREFACE .................................................... ii
 1. INTRODUCTION ........................................... 1
 1.1. Scope ............................................ 1
 1.2. Communication Framework .......................... 2
 2. NOTATIONAL CONVENTIONS ................................. 3
 3. LEXICAL ANALYSIS OF MESSAGES ........................... 5
 3.1. General Description .............................. 5
 3.2. Header Field Definitions ......................... 9
 3.3. Lexical Tokens ................................... 10
 3.4. Clarifications ................................... 11
 4. MESSAGE SPECIFICATION .................................. 17
 4.1. Syntax ........................................... 17
 4.2. Forwarding ....................................... 19
 4.3. Trace Fields ..................................... 20
 4.4. Originator Fields ................................ 21
 4.5. Receiver Fields .................................. 23
 4.6. Reference Fields ................................. 23
 4.7. Other Fields ..................................... 24
 5. DATE AND TIME SPECIFICATION ............................ 26
 5.1. Syntax ........................................... 26
 5.2. Semantics ........................................ 26
 6. ADDRESS SPECIFICATION .................................. 27
 6.1. Syntax ........................................... 27
 6.2. Semantics ........................................ 27
 6.3. Reserved Address ................................. 33
 7. BIBLIOGRAPHY ........................................... 34
 APPENDIX
 A. EXAMPLES ............................................... 36
 B. SIMPLE FIELD PARSING ................................... 40
 C. DIFFERENCES FROM RFC #733 .............................. 41
 D. ALPHABETICAL LISTING OF SYNTAX RULES ................... 44
 August 13, 1982 - i - RFC #822
 Standard for ARPA Internet Text Messages
 PREFACE
 By 1977, the Arpanet employed several informal standards for
 the text messages (mail) sent among its host computers. It was
 felt necessary to codify these practices and provide for those
 features that seemed imminent. The result of that effort was
 Request for Comments (RFC) #733, "Standard for the Format of ARPA
 Network Text Message", by Crocker, Vittal, Pogran, and Henderson.
 The specification attempted to avoid major changes in existing
 software, while permitting several new features.
 This document revises the specifications in RFC #733, in
 order to serve the needs of the larger and more complex ARPA
 Internet. Some of RFC #733's features failed to gain adequate
 acceptance. In order to simplify the standard and the software
 that follows it, these features have been removed. A different
 addressing scheme is used, to handle the case of inter-network
 mail; and the concept of re-transmission has been introduced.
 This specification is intended for use in the ARPA Internet.
 However, an attempt has been made to free it of any dependence on
 that environment, so that it can be applied to other network text
 message systems.
 The specification of RFC #733 took place over the course of
 one year, using the ARPANET mail environment, itself, to provide
 an on-going forum for discussing the capabilities to be included.
 More than twenty individuals, from across the country, partici-
 pated in the original discussion. The development of this
 revised specification has, similarly, utilized network mail-based
 group discussion. Both specification efforts greatly benefited
 from the comments and ideas of the participants.
 The syntax of the standard, in RFC #733, was originally
 specified in the Backus-Naur Form (BNF) meta-language. Ken L.
 Harrenstien, of SRI International, was responsible for re-coding
 the BNF into an augmented BNF that makes the representation
 smaller and easier to understand.
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 Standard for ARPA Internet Text Messages
 1. INTRODUCTION
 1.1. SCOPE
 This standard specifies a syntax for text messages that are
 sent among computer users, within the framework of "electronic
 mail". The standard supersedes the one specified in ARPANET
 Request for Comments #733, "Standard for the Format of ARPA Net-
 work Text Messages".
 In this context, messages are viewed as having an envelope
 and contents. The envelope contains whatever information is
 needed to accomplish transmission and delivery. The contents
 compose the object to be delivered to the recipient. This stan-
 dard applies only to the format and some of the semantics of mes-
 sage contents. It contains no specification of the information
 in the envelope.
 However, some message systems may use information from the
 contents to create the envelope. It is intended that this stan-
 dard facilitate the acquisition of such information by programs.
 Some message systems may store messages in formats that
 differ from the one specified in this standard. This specifica-
 tion is intended strictly as a definition of what message content
 format is to be passed BETWEEN hosts.
 Note: This standard is NOT intended to dictate the internal for-
 mats used by sites, the specific message system features
 that they are expected to support, or any of the charac-
 teristics of user interface programs that create or read
 messages.
 A distinction should be made between what the specification
 REQUIRES and what it ALLOWS. Messages can be made complex and
 rich with formally-structured components of information or can be
 kept small and simple, with a minimum of such information. Also,
 the standard simplifies the interpretation of differing visual
 formats in messages; only the visual aspect of a message is
 affected and not the interpretation of information within it.
 Implementors may choose to retain such visual distinctions.
 The formal definition is divided into four levels. The bot-
 tom level describes the meta-notation used in this document. The
 second level describes basic lexical analyzers that feed tokens
 to higher-level parsers. Next is an overall specification for
 messages; it permits distinguishing individual fields. Finally,
 there is definition of the contents of several structured fields.
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 Standard for ARPA Internet Text Messages
 1.2. COMMUNICATION FRAMEWORK
 Messages consist of lines of text. No special provisions
 are made for encoding drawings, facsimile, speech, or structured
 text. No significant consideration has been given to questions
 of data compression or to transmission and storage efficiency,
 and the standard tends to be free with the number of bits con-
 sumed. For example, field names are specified as free text,
 rather than special terse codes.
 A general "memo" framework is used. That is, a message con-
 sists of some information in a rigid format, followed by the main
 part of the message, with a format that is not specified in this
 document. The syntax of several fields of the rigidly-formated
 ("headers") section is defined in this specification; some of
 these fields must be included in all messages.
 The syntax that distinguishes between header fields is
 specified separately from the internal syntax for particular
 fields. This separation is intended to allow simple parsers to
 operate on the general structure of messages, without concern for
 the detailed structure of individual header fields. Appendix B
 is provided to facilitate construction of these parsers.
 In addition to the fields specified in this document, it is
 expected that other fields will gain common use. As necessary,
 the specifications for these "extension-fields" will be published
 through the same mechanism used to publish this document. Users
 may also wish to extend the set of fields that they use
 privately. Such "user-defined fields" are permitted.
 The framework severely constrains document tone and appear-
 ance and is primarily useful for most intra-organization communi-
 cations and well-structured inter-organization communication.
 It also can be used for some types of inter-process communica-
 tion, such as simple file transfer and remote job entry. A more
 robust framework might allow for multi-font, multi-color, multi-
 dimension encoding of information. A less robust one, as is
 present in most single-machine message systems, would more
 severely constrain the ability to add fields and the decision to
 include specific fields. In contrast with paper-based communica-
 tion, it is interesting to note that the RECEIVER of a message
 can exercise an extraordinary amount of control over the
 message's appearance. The amount of actual control available to
 message receivers is contingent upon the capabilities of their
 individual message systems.
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 2. NOTATIONAL CONVENTIONS
 This specification uses an augmented Backus-Naur Form (BNF)
 notation. The differences from standard BNF involve naming rules
 and indicating repetition and "local" alternatives.
 2.1. RULE NAMING
 Angle brackets ("<", ">") are not used, in general. The
 name of a rule is simply the name itself, rather than "<name>".
 Quotation-marks enclose literal text (which may be upper and/or
 lower case). Certain basic rules are in uppercase, such as
 SPACE, TAB, CRLF, DIGIT, ALPHA, etc. Angle brackets are used in
 rule definitions, and in the rest of this document, whenever
 their presence will facilitate discerning the use of rule names.
 2.2. RULE1 / RULE2: ALTERNATIVES
 Elements separated by slash ("/") are alternatives. There-
 fore "foo / bar" will accept foo or bar.
 2.3. (RULE1 RULE2): LOCAL ALTERNATIVES
 Elements enclosed in parentheses are treated as a single
 element. Thus, "(elem (foo / bar) elem)" allows the token
 sequences "elem foo elem" and "elem bar elem".
 2.4. *RULE: REPETITION
 The character "*" preceding an element indicates repetition.
 The full form is:
 <l>*<m>element
 indicating at least <l> and at most <m> occurrences of element.
 Default values are 0 and infinity so that "*(element)" allows any
 number, including zero; "1*element" requires at least one; and
 "1*2element" allows one or two.
 2.5. [RULE]: OPTIONAL
 Square brackets enclose optional elements; "[foo bar]" is
 equivalent to "*1(foo bar)".
 2.6. NRULE: SPECIFIC REPETITION
 "<n>(element)" is equivalent to "<n>*<n>(element)"; that is,
 exactly <n> occurrences of (element). Thus 2DIGIT is a 2-digit
 number, and 3ALPHA is a string of three alphabetic characters.
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 2.7. #RULE: LISTS
 A construct "#" is defined, similar to "*", as follows:
 <l>#<m>element
 indicating at least <l> and at most <m> elements, each separated
 by one or more commas (","). This makes the usual form of lists
 very easy; a rule such as '(element *("," element))' can be shown
 as "1#element". Wherever this construct is used, null elements
 are allowed, but do not contribute to the count of elements
 present. That is, "(element),,(element)" is permitted, but
 counts as only two elements. Therefore, where at least one ele-
 ment is required, at least one non-null element must be present.
 Default values are 0 and infinity so that "#(element)" allows any
 number, including zero; "1#element" requires at least one; and
 "1#2element" allows one or two.
 2.8. ; COMMENTS
 A semi-colon, set off some distance to the right of rule
 text, starts a comment that continues to the end of line. This
 is a simple way of including useful notes in parallel with the
 specifications.
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 3. LEXICAL ANALYSIS OF MESSAGES
 3.1. GENERAL DESCRIPTION
 A message consists of header fields and, optionally, a body.
 The body is simply a sequence of lines containing ASCII charac-
 ters. It is separated from the headers by a null line (i.e., a
 line with nothing preceding the CRLF).
 3.1.1. LONG HEADER FIELDS
 Each header field can be viewed as a single, logical line of
 ASCII characters, comprising a field-name and a field-body.
 For convenience, the field-body portion of this conceptual
 entity can be split into a multiple-line representation; this
 is called "folding". The general rule is that wherever there
 may be linear-white-space (NOT simply LWSP-chars), a CRLF
 immediately followed by AT LEAST one LWSP-char may instead be
 inserted. Thus, the single line
 To: "Joe & J. Harvey" <ddd @Org>, JJV @ BBN
 can be represented as:
 To: "Joe & J. Harvey" <ddd @ Org>,
 JJV@BBN
 and
 To: "Joe & J. Harvey"
 <ddd@ Org>, JJV
 @BBN
 and
 To: "Joe &
 J. Harvey" <ddd @ Org>, JJV @ BBN
 The process of moving from this folded multiple-line
 representation of a header field to its single line represen-
 tation is called "unfolding". Unfolding is accomplished by
 regarding CRLF immediately followed by a LWSP-char as
 equivalent to the LWSP-char.
 Note: While the standard permits folding wherever linear-
 white-space is permitted, it is recommended that struc-
 tured fields, such as those containing addresses, limit
 folding to higher-level syntactic breaks. For address
 fields, it is recommended that such folding occur
 August 13, 1982 - 5 - RFC #822
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 between addresses, after the separating comma.
 3.1.2. STRUCTURE OF HEADER FIELDS
 Once a field has been unfolded, it may be viewed as being com-
 posed of a field-name followed by a colon (":"), followed by a
 field-body, and terminated by a carriage-return/line-feed.
 The field-name must be composed of printable ASCII characters
 (i.e., characters that have values between 33. and 126.,
 decimal, except colon). The field-body may be composed of any
 ASCII characters, except CR or LF. (While CR and/or LF may be
 present in the actual text, they are removed by the action of
 unfolding the field.)
 Certain field-bodies of headers may be interpreted according
 to an internal syntax that some systems may wish to parse.
 These fields are called "structured fields". Examples
 include fields containing dates and addresses. Other fields,
 such as "Subject" and "Comments", are regarded simply as
 strings of text.
 Note: Any field which has a field-body that is defined as
 other than simply <text> is to be treated as a struc-
 tured field.
 Field-names, unstructured field bodies and structured
 field bodies each are scanned by their own, independent
 "lexical" analyzers.
 3.1.3. UNSTRUCTURED FIELD BODIES
 For some fields, such as "Subject" and "Comments", no struc-
 turing is assumed, and they are treated simply as <text>s, as
 in the message body. Rules of folding apply to these fields,
 so that such field bodies which occupy several lines must
 therefore have the second and successive lines indented by at
 least one LWSP-char.
 3.1.4. STRUCTURED FIELD BODIES
 To aid in the creation and reading of structured fields, the
 free insertion of linear-white-space (which permits folding
 by inclusion of CRLFs) is allowed between lexical tokens.
 Rather than obscuring the syntax specifications for these
 structured fields with explicit syntax for this linear-white-
 space, the existence of another "lexical" analyzer is assumed.
 This analyzer does not apply for unstructured field bodies
 that are simply strings of text, as described above. The
 analyzer provides an interpretation of the unfolded text
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 composing the body of the field as a sequence of lexical sym-
 bols.
 These symbols are:
 - individual special characters
 - quoted-strings
 - domain-literals
 - comments
 - atoms
 The first four of these symbols are self-delimiting. Atoms
 are not; they are delimited by the self-delimiting symbols and
 by linear-white-space. For the purposes of regenerating
 sequences of atoms and quoted-strings, exactly one SPACE is
 assumed to exist, and should be used, between them. (Also, in
 the "Clarifications" section on "White Space", below, note the
 rules about treatment of multiple contiguous LWSP-chars.)
 So, for example, the folded body of an address field
 ":sysmail"@ Some-Group. Some-Org,
 Muhammed.(I am the greatest) Ali @(the)Vegas.WBA
 August 13, 1982 - 7 - RFC #822
 Standard for ARPA Internet Text Messages
 is analyzed into the following lexical symbols and types:
 :sysmail quoted string
 @ special
 Some-Group atom
 . special
 Some-Org atom
 , special
 Muhammed atom
 . special
 (I am the greatest) comment
 Ali atom
 @ atom
 (the) comment
 Vegas atom
 . special
 WBA atom
 The canonical representations for the data in these addresses
 are the following strings:
 ":sysmail"@Some-Group.Some-Org
 and
 Muhammed.Ali@Vegas.WBA
 Note: For purposes of display, and when passing such struc-
 tured information to other systems, such as mail proto-
 col services, there must be NO linear-white-space
 between <word>s that are separated by period (".") or
 at-sign ("@") and exactly one SPACE between all other
 <word>s. Also, headers should be in a folded form.
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 Standard for ARPA Internet Text Messages
 3.2. HEADER FIELD DEFINITIONS
 These rules show a field meta-syntax, without regard for the
 particular type or internal syntax. Their purpose is to permit
 detection of fields; also, they present to higher-level parsers
 an image of each field as fitting on one line.
 field = field-name ":" [ field-body ] CRLF
 field-name = 1*<any CHAR, excluding CTLs, SPACE, and ":">
 field-body = field-body-contents
 [CRLF LWSP-char field-body]
 field-body-contents =
 <the ASCII characters making up the field-body, as
 defined in the following sections, and consisting
 of combinations of atom, quoted-string, and
 specials tokens, or else consisting of texts>
 August 13, 1982 - 9 - RFC #822
 Standard for ARPA Internet Text Messages
 3.3. LEXICAL TOKENS
 The following rules are used to define an underlying lexical
 analyzer, which feeds tokens to higher level parsers. See the
 ANSI references, in the Bibliography.
 ; ( Octal, Decimal.)
 CHAR = <any ASCII character> ; ( 0-177, 0.-127.)
 ALPHA = <any ASCII alphabetic character>
 ; (101-132, 65.- 90.)
 ; (141-172, 97.-122.)
 DIGIT = <any ASCII decimal digit> ; ( 60- 71, 48.- 57.)
 CTL = <any ASCII control ; ( 0- 37, 0.- 31.)
 character and DEL> ; ( 177, 127.)
 CR = <ASCII CR, carriage return> ; ( 15, 13.)
 LF = <ASCII LF, linefeed> ; ( 12, 10.)
 SPACE = <ASCII SP, space> ; ( 40, 32.)
 HTAB = <ASCII HT, horizontal-tab> ; ( 11, 9.)
 <"> = <ASCII quote mark> ; ( 42, 34.)
 CRLF = CR LF
 LWSP-char = SPACE / HTAB ; semantics = SPACE
 linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE
 ; CRLF => folding
 specials = "(" / ")" / "<" / ">" / "@" ; Must be in quoted-
 / "," / ";" / ":" / "\" / <"> ; string, to use
 / "." / "[" / "]" ; within a word.
 delimiters = specials / linear-white-space / comment
 text = <any CHAR, including bare ; => atoms, specials,
 CR & bare LF, but NOT ; comments and
 including CRLF> ; quoted-strings are
 ; NOT recognized.
 atom = 1*<any CHAR except specials, SPACE and CTLs>
 quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or
 ; quoted chars.
 qtext = <any CHAR excepting <">, ; => may be folded
 "\" & CR, and including
 linear-white-space>
 domain-literal = "[" *(dtext / quoted-pair) "]"
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 Standard for ARPA Internet Text Messages
 dtext = <any CHAR excluding "[", ; => may be folded
 "]", "\" & CR, & including
 linear-white-space>
 comment = "(" *(ctext / quoted-pair / comment) ")"
 ctext = <any CHAR excluding "(", ; => may be folded
 ")", "\" & CR, & including
 linear-white-space>
 quoted-pair = "\" CHAR ; may quote any char
 phrase = 1*word ; Sequence of words
 word = atom / quoted-string
 3.4. CLARIFICATIONS
 3.4.1. QUOTING
 Some characters are reserved for special interpretation, such
 as delimiting lexical tokens. To permit use of these charac-
 ters as uninterpreted data, a quoting mechanism is provided.
 To quote a character, precede it with a backslash ("\").
 This mechanism is not fully general. Characters may be quoted
 only within a subset of the lexical constructs. In particu-
 lar, quoting is limited to use within:
 - quoted-string
 - domain-literal
 - comment
 Within these constructs, quoting is REQUIRED for CR and "\"
 and for the character(s) that delimit the token (e.g., "(" and
 ")" for a comment). However, quoting is PERMITTED for any
 character.
 Note: In particular, quoting is NOT permitted within atoms.
 For example when the local-part of an addr-spec must
 contain a special character, a quoted string must be
 used. Therefore, a specification such as:
 Full\ Name@Domain
 is not legal and must be specified as:
 "Full Name"@Domain
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 Standard for ARPA Internet Text Messages
 3.4.2. WHITE SPACE
 Note: In structured field bodies, multiple linear space ASCII
 characters (namely HTABs and SPACEs) are treated as
 single spaces and may freely surround any symbol. In
 all header fields, the only place in which at least one
 LWSP-char is REQUIRED is at the beginning of continua-
 tion lines in a folded field.
 When passing text to processes that do not interpret text
 according to this standard (e.g., mail protocol servers), then
 NO linear-white-space characters should occur between a period
 (".") or at-sign ("@") and a <word>. Exactly ONE SPACE should
 be used in place of arbitrary linear-white-space and comment
 sequences.
 Note: Within systems conforming to this standard, wherever a
 member of the list of delimiters is allowed, LWSP-chars
 may also occur before and/or after it.
 Writers of mail-sending (i.e., header-generating) programs
 should realize that there is no network-wide definition of the
 effect of ASCII HT (horizontal-tab) characters on the appear-
 ance of text at another network host; therefore, the use of
 tabs in message headers, though permitted, is discouraged.
 3.4.3. COMMENTS
 A comment is a set of ASCII characters, which is enclosed in
 matching parentheses and which is not within a quoted-string
 The comment construct permits message originators to add text
 which will be useful for human readers, but which will be
 ignored by the formal semantics. Comments should be retained
 while the message is subject to interpretation according to
 this standard. However, comments must NOT be included in
 other cases, such as during protocol exchanges with mail
 servers.
 Comments nest, so that if an unquoted left parenthesis occurs
 in a comment string, there must also be a matching right
 parenthesis. When a comment acts as the delimiter between a
 sequence of two lexical symbols, such as two atoms, it is lex-
 ically equivalent with a single SPACE, for the purposes of
 regenerating the sequence, such as when passing the sequence
 onto a mail protocol server. Comments are detected as such
 only within field-bodies of structured fields.
 If a comment is to be "folded" onto multiple lines, then the
 syntax for folding must be adhered to. (See the "Lexical
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 Standard for ARPA Internet Text Messages
 Analysis of Messages" section on "Folding Long Header Fields"
 above, and the section on "Case Independence" below.) Note
 that the official semantics therefore do not "see" any
 unquoted CRLFs that are in comments, although particular pars-
 ing programs may wish to note their presence. For these pro-
 grams, it would be reasonable to interpret a "CRLF LWSP-char"
 as being a CRLF that is part of the comment; i.e., the CRLF is
 kept and the LWSP-char is discarded. Quoted CRLFs (i.e., a
 backslash followed by a CR followed by a LF) still must be
 followed by at least one LWSP-char.
 3.4.4. DELIMITING AND QUOTING CHARACTERS
 The quote character (backslash) and characters that delimit
 syntactic units are not, generally, to be taken as data that
 are part of the delimited or quoted unit(s). In particular,
 the quotation-marks that define a quoted-string, the
 parentheses that define a comment and the backslash that
 quotes a following character are NOT part of the quoted-
 string, comment or quoted character. A quotation-mark that is
 to be part of a quoted-string, a parenthesis that is to be
 part of a comment and a backslash that is to be part of either
 must each be preceded by the quote-character backslash ("\").
 Note that the syntax allows any character to be quoted within
 a quoted-string or comment; however only certain characters
 MUST be quoted to be included as data. These characters are
 the ones that are not part of the alternate text group (i.e.,
 ctext or qtext).
 The one exception to this rule is that a single SPACE is
 assumed to exist between contiguous words in a phrase, and
 this interpretation is independent of the actual number of
 LWSP-chars that the creator places between the words. To
 include more than one SPACE, the creator must make the LWSP-
 chars be part of a quoted-string.
 Quotation marks that delimit a quoted string and backslashes
 that quote the following character should NOT accompany the
 quoted-string when the string is passed to processes that do
 not interpret data according to this specification (e.g., mail
 protocol servers).
 3.4.5. QUOTED-STRINGS
 Where permitted (i.e., in words in structured fields) quoted-
 strings are treated as a single symbol. That is, a quoted-
 string is equivalent to an atom, syntactically. If a quoted-
 string is to be "folded" onto multiple lines, then the syntax
 for folding must be adhered to. (See the "Lexical Analysis of
 August 13, 1982 - 13 - RFC #822
 Standard for ARPA Internet Text Messages
 Messages" section on "Folding Long Header Fields" above, and
 the section on "Case Independence" below.) Therefore, the
 official semantics do not "see" any bare CRLFs that are in
 quoted-strings; however particular parsing programs may wish
 to note their presence. For such programs, it would be rea-
 sonable to interpret a "CRLF LWSP-char" as being a CRLF which
 is part of the quoted-string; i.e., the CRLF is kept and the
 LWSP-char is discarded. Quoted CRLFs (i.e., a backslash fol-
 lowed by a CR followed by a LF) are also subject to rules of
 folding, but the presence of the quoting character (backslash)
 explicitly indicates that the CRLF is data to the quoted
 string. Stripping off the first following LWSP-char is also
 appropriate when parsing quoted CRLFs.
 3.4.6. BRACKETING CHARACTERS
 There is one type of bracket which must occur in matched pairs
 and may have pairs nested within each other:
 o Parentheses ("(" and ")") are used to indicate com-
 ments.
 There are three types of brackets which must occur in matched
 pairs, and which may NOT be nested:
 o Colon/semi-colon (":" and ";") are used in address
 specifications to indicate that the included list of
 addresses are to be treated as a group.
 o Angle brackets ("<" and ">") are generally used to
 indicate the presence of a one machine-usable refer-
 ence (e.g., delimiting mailboxes), possibly including
 source-routing to the machine.
 o Square brackets ("[" and "]") are used to indicate the
 presence of a domain-literal, which the appropriate
 name-domain is to use directly, bypassing normal
 name-resolution mechanisms.
 3.4.7. CASE INDEPENDENCE
 Except as noted, alphabetic strings may be represented in any
 combination of upper and lower case. The only syntactic units
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 Standard for ARPA Internet Text Messages
 which requires preservation of case information are:
 - text
 - qtext
 - dtext
 - ctext
 - quoted-pair
 - local-part, except "Postmaster"
 When matching any other syntactic unit, case is to be ignored.
 For example, the field-names "From", "FROM", "from", and even
 "FroM" are semantically equal and should all be treated ident-
 ically.
 When generating these units, any mix of upper and lower case
 alphabetic characters may be used. The case shown in this
 specification is suggested for message-creating processes.
 Note: The reserved local-part address unit, "Postmaster", is
 an exception. When the value "Postmaster" is being
 interpreted, it must be accepted in any mixture of
 case, including "POSTMASTER", and "postmaster".
 3.4.8. FOLDING LONG HEADER FIELDS
 Each header field may be represented on exactly one line con-
 sisting of the name of the field and its body, and terminated
 by a CRLF; this is what the parser sees. For readability, the
 field-body portion of long header fields may be "folded" onto
 multiple lines of the actual field. "Long" is commonly inter-
 preted to mean greater than 65 or 72 characters. The former
 length serves as a limit, when the message is to be viewed on
 most simple terminals which use simple display software; how-
 ever, the limit is not imposed by this standard.
 Note: Some display software often can selectively fold lines,
 to suit the display terminal. In such cases, sender-
 provided folding can interfere with the display
 software.
 3.4.9. BACKSPACE CHARACTERS
 ASCII BS characters (Backspace, decimal 8) may be included in
 texts and quoted-strings to effect overstriking. However, any
 use of backspaces which effects an overstrike to the left of
 the beginning of the text or quoted-string is prohibited.
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 3.4.10. NETWORK-SPECIFIC TRANSFORMATIONS
 During transmission through heterogeneous networks, it may be
 necessary to force data to conform to a network's local con-
 ventions. For example, it may be required that a CR be fol-
 lowed either by LF, making a CRLF, or by <null>, if the CR is
 to stand alone). Such transformations are reversed, when the
 message exits that network.
 When crossing network boundaries, the message should be
 treated as passing through two modules. It will enter the
 first module containing whatever network-specific transforma-
 tions that were necessary to permit migration through the
 "current" network. It then passes through the modules:
 o Transformation Reversal
 The "current" network's idiosyncracies are removed and
 the message is returned to the canonical form speci-
 fied in this standard.
 o Transformation
 The "next" network's local idiosyncracies are imposed
 on the message.
 ------------------
 From ==> | Remove Net-A |
 Net-A | idiosyncracies |
 ------------------
 ||
 \/
 Conformance
 with standard
 ||
 \/
 ------------------
 | Impose Net-B | ==> To
 | idiosyncracies | Net-B
 ------------------
 August 13, 1982 - 16 - RFC #822
 Standard for ARPA Internet Text Messages
 4. MESSAGE SPECIFICATION
 4.1. SYNTAX
 Note: Due to an artifact of the notational conventions, the syn-
 tax indicates that, when present, some fields, must be in
 a particular order. Header fields are NOT required to
 occur in any particular order, except that the message
 body must occur AFTER the headers. It is recommended
 that, if present, headers be sent in the order "Return-
 Path", "Received", "Date", "From", "Subject", "Sender",
 "To", "cc", etc.
 This specification permits multiple occurrences of most
 fields. Except as noted, their interpretation is not
 specified here, and their use is discouraged.
 The following syntax for the bodies of various fields should
 be thought of as describing each field body as a single long
 string (or line). The "Lexical Analysis of Message" section on
 "Long Header Fields", above, indicates how such long strings can
 be represented on more than one line in the actual transmitted
 message.
 message = fields *( CRLF *text ) ; Everything after
 ; first null line
 ; is message body
 fields = dates ; Creation time,
 source ; author id & one
 1*destination ; address required
 *optional-field ; others optional
 source = [ trace ] ; net traversals
 originator ; original mail
 [ resent ] ; forwarded
 trace = return ; path to sender
 1*received ; receipt tags
 return = "Return-path" ":" route-addr ; return address
 received = "Received" ":" ; one per relay
 ["from" domain] ; sending host
 ["by" domain] ; receiving host
 ["via" atom] ; physical path
 *("with" atom) ; link/mail protocol
 ["id" msg-id] ; receiver msg id
 ["for" addr-spec] ; initial form
 August 13, 1982 - 17 - RFC #822
 Standard for ARPA Internet Text Messages
 ";" date-time ; time received
 originator = authentic ; authenticated addr
 [ "Reply-To" ":" 1#address] )
 authentic = "From" ":" mailbox ; Single author
 / ( "Sender" ":" mailbox ; Actual submittor
 "From" ":" 1#mailbox) ; Multiple authors
 ; or not sender
 resent = resent-authentic
 [ "Resent-Reply-To" ":" 1#address] )
 resent-authentic =
 = "Resent-From" ":" mailbox
 / ( "Resent-Sender" ":" mailbox
 "Resent-From" ":" 1#mailbox )
 dates = orig-date ; Original
 [ resent-date ] ; Forwarded
 orig-date = "Date" ":" date-time
 resent-date = "Resent-Date" ":" date-time
 destination = "To" ":" 1#address ; Primary
 / "Resent-To" ":" 1#address
 / "cc" ":" 1#address ; Secondary
 / "Resent-cc" ":" 1#address
 / "bcc" ":" #address ; Blind carbon
 / "Resent-bcc" ":" #address
 optional-field =
 / "Message-ID" ":" msg-id
 / "Resent-Message-ID" ":" msg-id
 / "In-Reply-To" ":" *(phrase / msg-id)
 / "References" ":" *(phrase / msg-id)
 / "Keywords" ":" #phrase
 / "Subject" ":" *text
 / "Comments" ":" *text
 / "Encrypted" ":" 1#2word
 / extension-field ; To be defined
 / user-defined-field ; May be pre-empted
 msg-id = "<" addr-spec ">" ; Unique message id
 August 13, 1982 - 18 - RFC #822
 Standard for ARPA Internet Text Messages
 extension-field =
 <Any field which is defined in a document
 published as a formal extension to this
 specification; none will have names beginning
 with the string "X-">
 user-defined-field =
 <Any field which has not been defined
 in this specification or published as an
 extension to this specification; names for
 such fields must be unique and may be
 pre-empted by published extensions>
 4.2. FORWARDING
 Some systems permit mail recipients to forward a message,
 retaining the original headers, by adding some new fields. This
 standard supports such a service, through the "Resent-" prefix to
 field names.
 Whenever the string "Resent-" begins a field name, the field
 has the same semantics as a field whose name does not have the
 prefix. However, the message is assumed to have been forwarded
 by an original recipient who attached the "Resent-" field. This
 new field is treated as being more recent than the equivalent,
 original field. For example, the "Resent-From", indicates the
 person that forwarded the message, whereas the "From" field indi-
 cates the original author.
 Use of such precedence information depends upon partici-
 pants' communication needs. For example, this standard does not
 dictate when a "Resent-From:" address should receive replies, in
 lieu of sending them to the "From:" address.
 Note: In general, the "Resent-" fields should be treated as con-
 taining a set of information that is independent of the
 set of original fields. Information for one set should
 not automatically be taken from the other. The interpre-
 tation of multiple "Resent-" fields, of the same type, is
 undefined.
 In the remainder of this specification, occurrence of legal
 "Resent-" fields are treated identically with the occurrence of
 August 13, 1982 - 19 - RFC #822
 Standard for ARPA Internet Text Messages
 fields whose names do not contain this prefix.
 4.3. TRACE FIELDS
 Trace information is used to provide an audit trail of mes-
 sage handling. In addition, it indicates a route back to the
 sender of the message.
 The list of known "via" and "with" values are registered
 with the Network Information Center, SRI International, Menlo
 Park, California.
 4.3.1. RETURN-PATH
 This field is added by the final transport system that
 delivers the message to its recipient. The field is intended
 to contain definitive information about the address and route
 back to the message's originator.
 Note: The "Reply-To" field is added by the originator and
 serves to direct replies, whereas the "Return-Path"
 field is used to identify a path back to the origina-
 tor.
 While the syntax indicates that a route specification is
 optional, every attempt should be made to provide that infor-
 mation in this field.
 4.3.2. RECEIVED
 A copy of this field is added by each transport service that
 relays the message. The information in the field can be quite
 useful for tracing transport problems.
 The names of the sending and receiving hosts and time-of-
 receipt may be specified. The "via" parameter may be used, to
 indicate what physical mechanism the message was sent over,
 such as Arpanet or Phonenet, and the "with" parameter may be
 used to indicate the mail-, or connection-, level protocol
 that was used, such as the SMTP mail protocol, or X.25 tran-
 sport protocol.
 Note: Several "with" parameters may be included, to fully
 specify the set of protocols that were used.
 Some transport services queue mail; the internal message iden-
 tifier that is assigned to the message may be noted, using the
 "id" parameter. When the sending host uses a destination
 address specification that the receiving host reinterprets, by
 August 13, 1982 - 20 - RFC #822
 Standard for ARPA Internet Text Messages
 expansion or transformation, the receiving host may wish to
 record the original specification, using the "for" parameter.
 For example, when a copy of mail is sent to the member of a
 distribution list, this parameter may be used to record the
 original address that was used to specify the list.
 4.4. ORIGINATOR FIELDS
 The standard allows only a subset of the combinations possi-
 ble with the From, Sender, Reply-To, Resent-From, Resent-Sender,
 and Resent-Reply-To fields. The limitation is intentional.
 4.4.1. FROM / RESENT-FROM
 This field contains the identity of the person(s) who wished
 this message to be sent. The message-creation process should
 default this field to be a single, authenticated machine
 address, indicating the AGENT (person, system or process)
 entering the message. If this is not done, the "Sender" field
 MUST be present. If the "From" field IS defaulted this way,
 the "Sender" field is optional and is redundant with the
 "From" field. In all cases, addresses in the "From" field
 must be machine-usable (addr-specs) and may not contain named
 lists (groups).
 4.4.2. SENDER / RESENT-SENDER
 This field contains the authenticated identity of the AGENT
 (person, system or process) that sends the message. It is
 intended for use when the sender is not the author of the mes-
 sage, or to indicate who among a group of authors actually
 sent the message. If the contents of the "Sender" field would
 be completely redundant with the "From" field, then the
 "Sender" field need not be present and its use is discouraged
 (though still legal). In particular, the "Sender" field MUST
 be present if it is NOT the same as the "From" Field.
 The Sender mailbox specification includes a word sequence
 which must correspond to a specific agent (i.e., a human user
 or a computer program) rather than a standard address. This
 indicates the expectation that the field will identify the
 single AGENT (person, system, or process) responsible for
 sending the mail and not simply include the name of a mailbox
 from which the mail was sent. For example in the case of a
 shared login name, the name, by itself, would not be adequate.
 The local-part address unit, which refers to this agent, is
 expected to be a computer system term, and not (for example) a
 generalized person reference which can be used outside the
 network text message context.
 August 13, 1982 - 21 - RFC #822
 Standard for ARPA Internet Text Messages
 Since the critical function served by the "Sender" field is
 identification of the agent responsible for sending mail and
 since computer programs cannot be held accountable for their
 behavior, it is strongly recommended that when a computer pro-
 gram generates a message, the HUMAN who is responsible for
 that program be referenced as part of the "Sender" field mail-
 box specification.
 4.4.3. REPLY-TO / RESENT-REPLY-TO
 This field provides a general mechanism for indicating any
 mailbox(es) to which responses are to be sent. Three typical
 uses for this feature can be distinguished. In the first
 case, the author(s) may not have regular machine-based mail-
 boxes and therefore wish(es) to indicate an alternate machine
 address. In the second case, an author may wish additional
 persons to be made aware of, or responsible for, replies. A
 somewhat different use may be of some help to "text message
 teleconferencing" groups equipped with automatic distribution
 services: include the address of that service in the "Reply-
 To" field of all messages submitted to the teleconference;
 then participants can "reply" to conference submissions to
 guarantee the correct distribution of any submission of their
 own.
 Note: The "Return-Path" field is added by the mail transport
 service, at the time of final deliver. It is intended
 to identify a path back to the orginator of the mes-
 sage. The "Reply-To" field is added by the message
 originator and is intended to direct replies.
 4.4.4. AUTOMATIC USE OF FROM / SENDER / REPLY-TO
 For systems which automatically generate address lists for
 replies to messages, the following recommendations are made:
 o The "Sender" field mailbox should be sent notices of
 any problems in transport or delivery of the original
 messages. If there is no "Sender" field, then the
 "From" field mailbox should be used.
 o The "Sender" field mailbox should NEVER be used
 automatically, in a recipient's reply message.
 o If the "Reply-To" field exists, then the reply should
 go to the addresses indicated in that field and not to
 the address(es) indicated in the "From" field.
 August 13, 1982 - 22 - RFC #822
 Standard for ARPA Internet Text Messages
 o If there is a "From" field, but no "Reply-To" field,
 the reply should be sent to the address(es) indicated
 in the "From" field.
 Sometimes, a recipient may actually wish to communicate with
 the person that initiated the message transfer. In such
 cases, it is reasonable to use the "Sender" address.
 This recommendation is intended only for automated use of
 originator-fields and is not intended to suggest that replies
 may not also be sent to other recipients of messages. It is
 up to the respective mail-handling programs to decide what
 additional facilities will be provided.
 Examples are provided in Appendix A.
 4.5. RECEIVER FIELDS
 4.5.1. TO / RESENT-TO
 This field contains the identity of the primary recipients of
 the message.
 4.5.2. CC / RESENT-CC
 This field contains the identity of the secondary (informa-
 tional) recipients of the message.
 4.5.3. BCC / RESENT-BCC
 This field contains the identity of additional recipients of
 the message. The contents of this field are not included in
 copies of the message sent to the primary and secondary reci-
 pients. Some systems may choose to include the text of the
 "Bcc" field only in the author(s)'s copy, while others may
 also include it in the text sent to all those indicated in the
 "Bcc" list.
 4.6. REFERENCE FIELDS
 4.6.1. MESSAGE-ID / RESENT-MESSAGE-ID
 This field contains a unique identifier (the local-part
 address unit) which refers to THIS version of THIS message.
 The uniqueness of the message identifier is guaranteed by the
 host which generates it. This identifier is intended to be
 machine readable and not necessarily meaningful to humans. A
 message identifier pertains to exactly one instantiation of a
 particular message; subsequent revisions to the message should
 August 13, 1982 - 23 - RFC #822
 Standard for ARPA Internet Text Messages
 each receive new message identifiers.
 4.6.2. IN-REPLY-TO
 The contents of this field identify previous correspon-
 dence which this message answers. Note that if message iden-
 tifiers are used in this field, they must use the msg-id
 specification format.
 4.6.3. REFERENCES
 The contents of this field identify other correspondence
 which this message references. Note that if message identif-
 iers are used, they must use the msg-id specification format.
 4.6.4. KEYWORDS
 This field contains keywords or phrases, separated by
 commas.
 4.7. OTHER FIELDS
 4.7.1. SUBJECT
 This is intended to provide a summary, or indicate the
 nature, of the message.
 4.7.2. COMMENTS
 Permits adding text comments onto the message without
 disturbing the contents of the message's body.
 4.7.3. ENCRYPTED
 Sometimes, data encryption is used to increase the
 privacy of message contents. If the body of a message has
 been encrypted, to keep its contents private, the "Encrypted"
 field can be used to note the fact and to indicate the nature
 of the encryption. The first <word> parameter indicates the
 software used to encrypt the body, and the second, optional
 <word> is intended to aid the recipient in selecting the
 proper decryption key. This code word may be viewed as an
 index to a table of keys held by the recipient.
 Note: Unfortunately, headers must contain envelope, as well
 as contents, information. Consequently, it is neces-
 sary that they remain unencrypted, so that mail tran-
 sport services may access them. Since names,
 addresses, and "Subject" field contents may contain
 August 13, 1982 - 24 - RFC #822
 Standard for ARPA Internet Text Messages
 sensitive information, this requirement limits total
 message privacy.
 Names of encryption software are registered with the Net-
 work Information Center, SRI International, Menlo Park, Cali-
 fornia.
 4.7.4. EXTENSION-FIELD
 A limited number of common fields have been defined in
 this document. As network mail requirements dictate, addi-
 tional fields may be standardized. To provide user-defined
 fields with a measure of safety, in name selection, such
 extension-fields will never have names that begin with the
 string "X-".
 Names of Extension-fields are registered with the Network
 Information Center, SRI International, Menlo Park, California.
 4.7.5. USER-DEFINED-FIELD
 Individual users of network mail are free to define and
 use additional header fields. Such fields must have names
 which are not already used in the current specification or in
 any definitions of extension-fields, and the overall syntax of
 these user-defined-fields must conform to this specification's
 rules for delimiting and folding fields. Due to the
 extension-field publishing process, the name of a user-
 defined-field may be pre-empted
 Note: The prefatory string "X-" will never be used in the
 names of Extension-fields. This provides user-defined
 fields with a protected set of names.
 August 13, 1982 - 25 - RFC #822
 Standard for ARPA Internet Text Messages
 5. DATE AND TIME SPECIFICATION
 5.1. SYNTAX
 date-time = [ day "," ] date time ; dd mm yy
 ; hh:mm:ss zzz
 day = "Mon" / "Tue" / "Wed" / "Thu"
 / "Fri" / "Sat" / "Sun"
 date = 1*2DIGIT month 2DIGIT ; day month year
 ; e.g. 20 Jun 82
 month = "Jan" / "Feb" / "Mar" / "Apr"
 / "May" / "Jun" / "Jul" / "Aug"
 / "Sep" / "Oct" / "Nov" / "Dec"
 time = hour zone ; ANSI and Military
 hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT]
 ; 00:00:00 - 23:59:59
 zone = "UT" / "GMT" ; Universal Time
 ; North American : UT
 / "EST" / "EDT" ; Eastern: - 5/ - 4
 / "CST" / "CDT" ; Central: - 6/ - 5
 / "MST" / "MDT" ; Mountain: - 7/ - 6
 / "PST" / "PDT" ; Pacific: - 8/ - 7
 / 1ALPHA ; Military: Z = UT;
 ; A:-1; (J not used)
 ; M:-12; N:+1; Y:+12
 / ( ("+" / "-") 4DIGIT ) ; Local differential
 ; hours+min. (HHMM)
 5.2. SEMANTICS
 If included, day-of-week must be the day implied by the date
 specification.
 Time zone may be indicated in several ways. "UT" is Univer-
 sal Time (formerly called "Greenwich Mean Time"); "GMT" is per-
 mitted as a reference to Universal Time. The military standard
 uses a single character for each zone. "Z" is Universal Time.
 "A" indicates one hour earlier, and "M" indicates 12 hours ear-
 lier; "N" is one hour later, and "Y" is 12 hours later. The
 letter "J" is not used. The other remaining two forms are taken
 from ANSI standard X3.51-1975. One allows explicit indication of
 the amount of offset from UT; the other uses common 3-character
 strings for indicating time zones in North America.
 August 13, 1982 - 26 - RFC #822
 Standard for ARPA Internet Text Messages
 6. ADDRESS SPECIFICATION
 6.1. SYNTAX
 address = mailbox ; one addressee
 / group ; named list
 group = phrase ":" [#mailbox] ";"
 mailbox = addr-spec ; simple address
 / phrase route-addr ; name & addr-spec
 route-addr = "<" [route] addr-spec ">"
 route = 1#("@" domain) ":" ; path-relative
 addr-spec = local-part "@" domain ; global address
 local-part = word *("." word) ; uninterpreted
 ; case-preserved
 domain = sub-domain *("." sub-domain)
 sub-domain = domain-ref / domain-literal
 domain-ref = atom ; symbolic reference
 6.2. SEMANTICS
 A mailbox receives mail. It is a conceptual entity which
 does not necessarily pertain to file storage. For example, some
 sites may choose to print mail on their line printer and deliver
 the output to the addressee's desk.
 A mailbox specification comprises a person, system or pro-
 cess name reference, a domain-dependent string, and a name-domain
 reference. The name reference is optional and is usually used to
 indicate the human name of a recipient. The name-domain refer-
 ence specifies a sequence of sub-domains. The domain-dependent
 string is uninterpreted, except by the final sub-domain; the rest
 of the mail service merely transmits it as a literal string.
 6.2.1. DOMAINS
 A name-domain is a set of registered (mail) names. A name-
 domain specification resolves to a subordinate name-domain
 specification or to a terminal domain-dependent string.
 Hence, domain specification is extensible, permitting any
 number of registration levels.
 August 13, 1982 - 27 - RFC #822
 Standard for ARPA Internet Text Messages
 Name-domains model a global, logical, hierarchical addressing
 scheme. The model is logical, in that an address specifica-
 tion is related to name registration and is not necessarily
 tied to transmission path. The model's hierarchy is a
 directed graph, called an in-tree, such that there is a single
 path from the root of the tree to any node in the hierarchy.
 If more than one path actually exists, they are considered to
 be different addresses.
 The root node is common to all addresses; consequently, it is
 not referenced. Its children constitute "top-level" name-
 domains. Usually, a service has access to its own full domain
 specification and to the names of all top-level name-domains.
 The "top" of the domain addressing hierarchy -- a child of the
 root -- is indicated by the right-most field, in a domain
 specification. Its child is specified to the left, its child
 to the left, and so on.
 Some groups provide formal registration services; these con-
 stitute name-domains that are independent logically of
 specific machines. In addition, networks and machines impli-
 citly compose name-domains, since their membership usually is
 registered in name tables.
 In the case of formal registration, an organization implements
 a (distributed) data base which provides an address-to-route
 mapping service for addresses of the form:
 person@registry.organization
 Note that "organization" is a logical entity, separate from
 any particular communication network.
 A mechanism for accessing "organization" is universally avail-
 able. That mechanism, in turn, seeks an instantiation of the
 registry; its location is not indicated in the address specif-
 ication. It is assumed that the system which operates under
 the name "organization" knows how to find a subordinate regis-
 try. The registry will then use the "person" string to deter-
 mine where to send the mail specification.
 The latter, network-oriented case permits simple, direct,
 attachment-related address specification, such as:
 user@host.network
 Once the network is accessed, it is expected that a message
 will go directly to the host and that the host will resolve
 August 13, 1982 - 28 - RFC #822
 Standard for ARPA Internet Text Messages
 the user name, placing the message in the user's mailbox.
 6.2.2. ABBREVIATED DOMAIN SPECIFICATION
 Since any number of levels is possible within the domain
 hierarchy, specification of a fully qualified address can
 become inconvenient. This standard permits abbreviated domain
 specification, in a special case:
 For the address of the sender, call the left-most
 sub-domain Level N. In a header address, if all of
 the sub-domains above (i.e., to the right of) Level N
 are the same as those of the sender, then they do not
 have to appear in the specification. Otherwise, the
 address must be fully qualified.
 This feature is subject to approval by local sub-
 domains. Individual sub-domains may require their
 member systems, which originate mail, to provide full
 domain specification only. When permitted, abbrevia-
 tions may be present only while the message stays
 within the sub-domain of the sender.
 Use of this mechanism requires the sender's sub-domain
 to reserve the names of all top-level domains, so that
 full specifications can be distinguished from abbrevi-
 ated specifications.
 For example, if a sender's address is:
 sender@registry-A.registry-1.organization-X
 and one recipient's address is:
 recipient@registry-B.registry-1.organization-X
 and another's is:
 recipient@registry-C.registry-2.organization-X
 then ".registry-1.organization-X" need not be specified in the
 the message, but "registry-C.registry-2" DOES have to be
 specified. That is, the first two addresses may be abbrevi-
 ated, but the third address must be fully specified.
 When a message crosses a domain boundary, all addresses must
 be specified in the full format, ending with the top-level
 name-domain in the right-most field. It is the responsibility
 of mail forwarding services to ensure that addresses conform
 August 13, 1982 - 29 - RFC #822
 Standard for ARPA Internet Text Messages
 with this requirement. In the case of abbreviated addresses,
 the relaying service must make the necessary expansions. It
 should be noted that it often is difficult for such a service
 to locate all occurrences of address abbreviations. For exam-
 ple, it will not be possible to find such abbreviations within
 the body of the message. The "Return-Path" field can aid
 recipients in recovering from these errors.
 Note: When passing any portion of an addr-spec onto a process
 which does not interpret data according to this stan-
 dard (e.g., mail protocol servers). There must be NO
 LWSP-chars preceding or following the at-sign or any
 delimiting period ("."), such as shown in the above
 examples, and only ONE SPACE between contiguous
 <word>s.
 6.2.3. DOMAIN TERMS
 A domain-ref must be THE official name of a registry, network,
 or host. It is a symbolic reference, within a name sub-
 domain. At times, it is necessary to bypass standard mechan-
 isms for resolving such references, using more primitive
 information, such as a network host address rather than its
 associated host name.
 To permit such references, this standard provides the domain-
 literal construct. Its contents must conform with the needs
 of the sub-domain in which it is interpreted.
 Domain-literals which refer to domains within the ARPA Inter-
 net specify 32-bit Internet addresses, in four 8-bit fields
 noted in decimal, as described in Request for Comments #820,
 "Assigned Numbers." For example:
 [10.0.3.19]
 Note: THE USE OF DOMAIN-LITERALS IS STRONGLY DISCOURAGED. It
 is permitted only as a means of bypassing temporary
 system limitations, such as name tables which are not
 complete.
 The names of "top-level" domains, and the names of domains
 under in the ARPA Internet, are registered with the Network
 Information Center, SRI International, Menlo Park, California.
 6.2.4. DOMAIN-DEPENDENT LOCAL STRING
 The local-part of an addr-spec in a mailbox specification
 (i.e., the host's name for the mailbox) is understood to be
 August 13, 1982 - 30 - RFC #822
 Standard for ARPA Internet Text Messages
 whatever the receiving mail protocol server allows. For exam-
 ple, some systems do not understand mailbox references of the
 form "P. D. Q. Bach", but others do.
 This specification treats periods (".") as lexical separators.
 Hence, their presence in local-parts which are not quoted-
 strings, is detected. However, such occurrences carry NO
 semantics. That is, if a local-part has periods within it, an
 address parser will divide the local-part into several tokens,
 but the sequence of tokens will be treated as one uninter-
 preted unit. The sequence will be re-assembled, when the
 address is passed outside of the system such as to a mail pro-
 tocol service.
 For example, the address:
 First.Last@Registry.Org
 is legal and does not require the local-part to be surrounded
 with quotation-marks. (However, "First Last" DOES require
 quoting.) The local-part of the address, when passed outside
 of the mail system, within the Registry.Org domain, is
 "First.Last", again without quotation marks.
 6.2.5. BALANCING LOCAL-PART AND DOMAIN
 In some cases, the boundary between local-part and domain can
 be flexible. The local-part may be a simple string, which is
 used for the final determination of the recipient's mailbox.
 All other levels of reference are, therefore, part of the
 domain.
 For some systems, in the case of abbreviated reference to the
 local and subordinate sub-domains, it may be possible to
 specify only one reference within the domain part and place
 the other, subordinate name-domain references within the
 local-part. This would appear as:
 mailbox.sub1.sub2@this-domain
 Such a specification would be acceptable to address parsers
 which conform to RFC #733, but do not support this newer
 Internet standard. While contrary to the intent of this stan-
 dard, the form is legal.
 Also, some sub-domains have a specification syntax which does
 not conform to this standard. For example:
 sub-net.mailbox@sub-domain.domain
 August 13, 1982 - 31 - RFC #822
 Standard for ARPA Internet Text Messages
 uses a different parsing sequence for local-part than for
 domain.
 Note: As a rule, the domain specification should contain
 fields which are encoded according to the syntax of
 this standard and which contain generally-standardized
 information. The local-part specification should con-
 tain only that portion of the address which deviates
 from the form or intention of the domain field.
 6.2.6. MULTIPLE MAILBOXES
 An individual may have several mailboxes and wish to receive
 mail at whatever mailbox is convenient for the sender to
 access. This standard does not provide a means of specifying
 "any member of" a list of mailboxes.
 A set of individuals may wish to receive mail as a single unit
 (i.e., a distribution list). The <group> construct permits
 specification of such a list. Recipient mailboxes are speci-
 fied within the bracketed part (":" - ";"). A copy of the
 transmitted message is to be sent to each mailbox listed.
 This standard does not permit recursive specification of
 groups within groups.
 While a list must be named, it is not required that the con-
 tents of the list be included. In this case, the <address>
 serves only as an indication of group distribution and would
 appear in the form:
 name:;
 Some mail services may provide a group-list distribution
 facility, accepting a single mailbox reference, expanding it
 to the full distribution list, and relaying the mail to the
 list's members. This standard provides no additional syntax
 for indicating such a service. Using the <group> address
 alternative, while listing one mailbox in it, can mean either
 that the mailbox reference will be expanded to a list or that
 there is a group with one member.
 6.2.7. EXPLICIT PATH SPECIFICATION
 At times, a message originator may wish to indicate the
 transmission path that a message should follow. This is
 called source routing. The normal addressing scheme, used in
 an addr-spec, is carefully separated from such information;
 the <route> portion of a route-addr is provided for such occa-
 sions. It specifies the sequence of hosts and/or transmission
 August 13, 1982 - 32 - RFC #822
 Standard for ARPA Internet Text Messages
 services that are to be traversed. Both domain-refs and
 domain-literals may be used.
 Note: The use of source routing is discouraged. Unless the
 sender has special need of path restriction, the choice
 of transmission route should be left to the mail tran-
 sport service.
 6.3. RESERVED ADDRESS
 It often is necessary to send mail to a site, without know-
 ing any of its valid addresses. For example, there may be mail
 system dysfunctions, or a user may wish to find out a person's
 correct address, at that site.
 This standard specifies a single, reserved mailbox address
 (local-part) which is to be valid at each site. Mail sent to
 that address is to be routed to a person responsible for the
 site's mail system or to a person with responsibility for general
 site operation. The name of the reserved local-part address is:
 Postmaster
 so that "Postmaster@domain" is required to be valid.
 Note: This reserved local-part must be matched without sensi-
 tivity to alphabetic case, so that "POSTMASTER", "postmas-
 ter", and even "poStmASteR" is to be accepted.
 August 13, 1982 - 33 - RFC #822
 Standard for ARPA Internet Text Messages
 7. BIBLIOGRAPHY
 ANSI. "USA Standard Code for Information Interchange," X3.4.
 American National Standards Institute: New York (1968). Also
 in: Feinler, E. and J. Postel, eds., "ARPANET Protocol Hand-
 book", NIC 7104.
 ANSI. "Representations of Universal Time, Local Time Differen-
 tials, and United States Time Zone References for Information
 Interchange," X3.51-1975. American National Standards Insti-
 tute: New York (1975).
 Bemer, R.W., "Time and the Computer." In: Interface Age (Feb.
 1979).
 Bennett, C.J. "JNT Mail Protocol". Joint Network Team, Ruther-
 ford and Appleton Laboratory: Didcot, England.
 Bhushan, A.K., Pogran, K.T., Tomlinson, R.S., and White, J.E.
 "Standardizing Network Mail Headers," ARPANET Request for
 Comments No. 561, Network Information Center No. 18516; SRI
 International: Menlo Park (September 1973).
 Birrell, A.D., Levin, R., Needham, R.M., and Schroeder, M.D.
 "Grapevine: An Exercise in Distributed Computing," Communica-
 tions of the ACM 25, 4 (April 1982), 260-274.
 Crocker, D.H., Vittal, J.J., Pogran, K.T., Henderson, D.A.
 "Standard for the Format of ARPA Network Text Message,"
 ARPANET Request for Comments No. 733, Network Information
 Center No. 41952. SRI International: Menlo Park (November
 1977).
 Feinler, E.J. and Postel, J.B. ARPANET Protocol Handbook, Net-
 work Information Center No. 7104 (NTIS AD A003890). SRI
 International: Menlo Park (April 1976).
 Harary, F. "Graph Theory". Addison-Wesley: Reading, Mass.
 (1969).
 Levin, R. and Schroeder, M. "Transport of Electronic Messages
 through a Network," TeleInformatics 79, pp. 29-33. North
 Holland (1979). Also as Xerox Palo Alto Research Center
 Technical Report CSL-79-4.
 Myer, T.H. and Henderson, D.A. "Message Transmission Protocol,"
 ARPANET Request for Comments, No. 680, Network Information
 Center No. 32116. SRI International: Menlo Park (1975).
 August 13, 1982 - 34 - RFC #822
 Standard for ARPA Internet Text Messages
 NBS. "Specification of Message Format for Computer Based Message
 Systems, Recommended Federal Information Processing Standard."
 National Bureau of Standards: Gaithersburg, Maryland
 (October 1981).
 NIC. Internet Protocol Transition Workbook. Network Information
 Center, SRI-International, Menlo Park, California (March
 1982).
 Oppen, D.C. and Dalal, Y.K. "The Clearinghouse: A Decentralized
 Agent for Locating Named Objects in a Distributed Environ-
 ment," OPD-T8103. Xerox Office Products Division: Palo Alto,
 CA. (October 1981).
 Postel, J.B. "Assigned Numbers," ARPANET Request for Comments,
 No. 820. SRI International: Menlo Park (August 1982).
 Postel, J.B. "Simple Mail Transfer Protocol," ARPANET Request
 for Comments, No. 821. SRI International: Menlo Park (August
 1982).
 Shoch, J.F. "Internetwork naming, addressing and routing," in
 Proc. 17th IEEE Computer Society International Conference, pp.
 72-79, Sept. 1978, IEEE Cat. No. 78 CH 1388-8C.
 Su, Z. and Postel, J. "The Domain Naming Convention for Internet
 User Applications," ARPANET Request for Comments, No. 819.
 SRI International: Menlo Park (August 1982).
 August 13, 1982 - 35 - RFC #822
 Standard for ARPA Internet Text Messages
 APPENDIX
 A. EXAMPLES
 A.1. ADDRESSES
 A.1.1. Alfred Neuman <Neuman@BBN-TENEXA>
 A.1.2. Neuman@BBN-TENEXA
 These two "Alfred Neuman" examples have identical seman-
 tics, as far as the operation of the local host's mail sending
 (distribution) program (also sometimes called its "mailer")
 and the remote host's mail protocol server are concerned. In
 the first example, the "Alfred Neuman" is ignored by the
 mailer, as "Neuman@BBN-TENEXA" completely specifies the reci-
 pient. The second example contains no superfluous informa-
 tion, and, again, "Neuman@BBN-TENEXA" is the intended reci-
 pient.
 Note: When the message crosses name-domain boundaries, then
 these specifications must be changed, so as to indicate
 the remainder of the hierarchy, starting with the top
 level.
 A.1.3. "George, Ted" <Shared@Group.Arpanet>
 This form might be used to indicate that a single mailbox
 is shared by several users. The quoted string is ignored by
 the originating host's mailer, because "Shared@Group.Arpanet"
 completely specifies the destination mailbox.
 A.1.4. Wilt . (the Stilt) Chamberlain@NBA.US
 The "(the Stilt)" is a comment, which is NOT included in
 the destination mailbox address handed to the originating
 system's mailer. The local-part of the address is the string
 "Wilt.Chamberlain", with NO space between the first and second
 words.
 A.1.5. Address Lists
 Gourmets: Pompous Person <WhoZiWhatZit@Cordon-Bleu>,
 Childs@WGBH.Boston, Galloping Gourmet@
 ANT.Down-Under (Australian National Television),
 Cheapie@Discount-Liquors;,
 Cruisers: Port@Portugal, Jones@SEA;,
 Another@Somewhere.SomeOrg
 August 13, 1982 - 36 - RFC #822
 Standard for ARPA Internet Text Messages
 This group list example points out the use of comments and the
 mixing of addresses and groups.
 A.2. ORIGINATOR ITEMS
 A.2.1. Author-sent
 George Jones logs into his host as "Jones". He sends
 mail himself.
 From: Jones@Group.Org
 or
 From: George Jones <Jones@Group.Org>
 A.2.2. Secretary-sent
 George Jones logs in as Jones on his host. His secre-
 tary, who logs in as Secy sends mail for him. Replies to the
 mail should go to George.
 From: George Jones <Jones@Group>
 Sender: Secy@Other-Group
 A.2.3. Secretary-sent, for user of shared directory
 George Jones' secretary sends mail for George. Replies
 should go to George.
 From: George Jones<Shared@Group.Org>
 Sender: Secy@Other-Group
 Note that there need not be a space between "Jones" and the
 "<", but adding a space enhances readability (as is the case
 in other examples.
 A.2.4. Committee activity, with one author
 George is a member of a committee. He wishes to have any
 replies to his message go to all committee members.
 From: George Jones <Jones@Host.Net>
 Sender: Jones@Host
 Reply-To: The Committee: Jones@Host.Net,
 Smith@Other.Org,
 Doe@Somewhere-Else;
 Note that if George had not included himself in the
 August 13, 1982 - 37 - RFC #822
 Standard for ARPA Internet Text Messages
 enumeration of The Committee, he would not have gotten an
 implicit reply; the presence of the "Reply-to" field SUPER-
 SEDES the sending of a reply to the person named in the "From"
 field.
 A.2.5. Secretary acting as full agent of author
 George Jones asks his secretary (Secy@Host) to send a
 message for him in his capacity as Group. He wants his secre-
 tary to handle all replies.
 From: George Jones <Group@Host>
 Sender: Secy@Host
 Reply-To: Secy@Host
 A.2.6. Agent for user without online mailbox
 A friend of George's, Sarah, is visiting. George's
 secretary sends some mail to a friend of Sarah in computer-
 land. Replies should go to George, whose mailbox is Jones at
 Registry.
 From: Sarah Friendly <Secy@Registry>
 Sender: Secy-Name <Secy@Registry>
 Reply-To: Jones@Registry.
 A.2.7. Agent for member of a committee
 George's secretary sends out a message which was authored
 jointly by all the members of a committee. Note that the name
 of the committee cannot be specified, since <group> names are
 not permitted in the From field.
 From: Jones@Host,
 Smith@Other-Host,
 Doe@Somewhere-Else
 Sender: Secy@SHost
 August 13, 1982 - 38 - RFC #822
 Standard for ARPA Internet Text Messages
 A.3. COMPLETE HEADERS
 A.3.1. Minimum required
 Date: 26 Aug 76 1429 EDT Date: 26 Aug 76 1429 EDT
 From: Jones@Registry.Org or From: Jones@Registry.Org
 Bcc: To: Smith@Registry.Org
 Note that the "Bcc" field may be empty, while the "To" field
 is required to have at least one address.
 A.3.2. Using some of the additional fields
 Date: 26 Aug 76 1430 EDT
 From: George Jones<Group@Host>
 Sender: Secy@SHOST
 To: "Al Neuman"@Mad-Host,
 Sam.Irving@Other-Host
 Message-ID: <some.string@SHOST>
 A.3.3. About as complex as you're going to get
 Date : 27 Aug 76 0932 PDT
 From : Ken Davis <KDavis@This-Host.This-net>
 Subject : Re: The Syntax in the RFC
 Sender : KSecy@Other-Host
 Reply-To : Sam.Irving@Reg.Organization
 To : George Jones <Group@Some-Reg.An-Org>,
 Al.Neuman@MAD.Publisher
 cc : Important folk:
 Tom Softwood <Balsa@Tree.Root>,
 "Sam Irving"@Other-Host;,
 Standard Distribution:
 /main/davis/people/standard@Other-Host,
 "<Jones>standard.dist.3"@Tops-20-Host>;
 Comment : Sam is away on business. He asked me to handle
 his mail for him. He'll be able to provide a
 more accurate explanation when he returns
 next week.
 In-Reply-To: <some.string@DBM.Group>, George's message
 X-Special-action: This is a sample of user-defined field-
 names. There could also be a field-name
 "Special-action", but its name might later be
 preempted
 Message-ID: <4231.629.XYzi-What@Other-Host>
 August 13, 1982 - 39 - RFC #822
 Standard for ARPA Internet Text Messages
 B. SIMPLE FIELD PARSING
 Some mail-reading software systems may wish to perform only
 minimal processing, ignoring the internal syntax of structured
 field-bodies and treating them the same as unstructured-field-
 bodies. Such software will need only to distinguish:
 o Header fields from the message body,
 o Beginnings of fields from lines which continue fields,
 o Field-names from field-contents.
 The abbreviated set of syntactic rules which follows will
 suffice for this purpose. It describes a limited view of mes-
 sages and is a subset of the syntactic rules provided in the main
 part of this specification. One small exception is that the con-
 tents of field-bodies consist only of text:
 B.1. SYNTAX
 message = *field *(CRLF *text)
 field = field-name ":" [field-body] CRLF
 field-name = 1*<any CHAR, excluding CTLs, SPACE, and ":">
 field-body = *text [CRLF LWSP-char field-body]
 B.2. SEMANTICS
 Headers occur before the message body and are terminated by
 a null line (i.e., two contiguous CRLFs).
 A line which continues a header field begins with a SPACE or
 HTAB character, while a line beginning a field starts with a
 printable character which is not a colon.
 A field-name consists of one or more printable characters
 (excluding colon, space, and control-characters). A field-name
 MUST be contained on one line. Upper and lower case are not dis-
 tinguished when comparing field-names.
 August 13, 1982 - 40 - RFC #822
 Standard for ARPA Internet Text Messages
 C. DIFFERENCES FROM RFC #733
 The following summarizes the differences between this stan-
 dard and the one specified in Arpanet Request for Comments #733,
 "Standard for the Format of ARPA Network Text Messages". The
 differences are listed in the order of their occurrence in the
 current specification.
 C.1. FIELD DEFINITIONS
 C.1.1. FIELD NAMES
 These now must be a sequence of printable characters. They
 may not contain any LWSP-chars.
 C.2. LEXICAL TOKENS
 C.2.1. SPECIALS
 The characters period ("."), left-square bracket ("["), and
 right-square bracket ("]") have been added. For presentation
 purposes, and when passing a specification to a system that
 does not conform to this standard, periods are to be contigu-
 ous with their surrounding lexical tokens. No linear-white-
 space is permitted between them. The presence of one LWSP-
 char between other tokens is still directed.
 C.2.2. ATOM
 Atoms may not contain SPACE.
 C.2.3. SPECIAL TEXT
 ctext and qtext have had backslash ("\") added to the list of
 prohibited characters.
 C.2.4. DOMAINS
 The lexical tokens <domain-literal> and <dtext> have been
 added.
 C.3. MESSAGE SPECIFICATION
 C.3.1. TRACE
 The "Return-path:" and "Received:" fields have been specified.
 August 13, 1982 - 41 - RFC #822
 Standard for ARPA Internet Text Messages
 C.3.2. FROM
 The "From" field must contain machine-usable addresses (addr-
 spec). Multiple addresses may be specified, but named-lists
 (groups) may not.
 C.3.3. RESENT
 The meta-construct of prefacing field names with the string
 "Resent-" has been added, to indicate that a message has been
 forwarded by an intermediate recipient.
 C.3.4. DESTINATION
 A message must contain at least one destination address field.
 "To" and "CC" are required to contain at least one address.
 C.3.5. IN-REPLY-TO
 The field-body is no longer a comma-separated list, although a
 sequence is still permitted.
 C.3.6. REFERENCE
 The field-body is no longer a comma-separated list, although a
 sequence is still permitted.
 C.3.7. ENCRYPTED
 A field has been specified that permits senders to indicate
 that the body of a message has been encrypted.
 C.3.8. EXTENSION-FIELD
 Extension fields are prohibited from beginning with the char-
 acters "X-".
 C.4. DATE AND TIME SPECIFICATION
 C.4.1. SIMPLIFICATION
 Fewer optional forms are permitted and the list of three-
 letter time zones has been shortened.
 C.5. ADDRESS SPECIFICATION
 August 13, 1982 - 42 - RFC #822
 Standard for ARPA Internet Text Messages
 C.5.1. ADDRESS
 The use of quoted-string, and the ":"-atom-":" construct, have
 been removed. An address now is either a single mailbox
 reference or is a named list of addresses. The latter indi-
 cates a group distribution.
 C.5.2. GROUPS
 Group lists are now required to to have a name. Group lists
 may not be nested.
 C.5.3. MAILBOX
 A mailbox specification may indicate a person's name, as
 before. Such a named list no longer may specify multiple
 mailboxes and may not be nested.
 C.5.4. ROUTE ADDRESSING
 Addresses now are taken to be absolute, global specifications,
 independent of transmission paths. The <route> construct has
 been provided, to permit explicit specification of transmis-
 sion path. RFC #733's use of multiple at-signs ("@") was
 intended as a general syntax for indicating routing and/or
 hierarchical addressing. The current standard separates these
 specifications and only one at-sign is permitted.
 C.5.5. AT-SIGN
 The string " at " no longer is used as an address delimiter.
 Only at-sign ("@") serves the function.
 C.5.6. DOMAINS
 Hierarchical, logical name-domains have been added.
 C.6. RESERVED ADDRESS
 The local-part "Postmaster" has been reserved, so that users can
 be guaranteed at least one valid address at a site.
 August 13, 1982 - 43 - RFC #822
 Standard for ARPA Internet Text Messages
 D. ALPHABETICAL LISTING OF SYNTAX RULES
 address = mailbox ; one addressee
 / group ; named list
 addr-spec = local-part "@" domain ; global address
 ALPHA = <any ASCII alphabetic character>
 ; (101-132, 65.- 90.)
 ; (141-172, 97.-122.)
 atom = 1*<any CHAR except specials, SPACE and CTLs>
 authentic = "From" ":" mailbox ; Single author
 / ( "Sender" ":" mailbox ; Actual submittor
 "From" ":" 1#mailbox) ; Multiple authors
 ; or not sender
 CHAR = <any ASCII character> ; ( 0-177, 0.-127.)
 comment = "(" *(ctext / quoted-pair / comment) ")"
 CR = <ASCII CR, carriage return> ; ( 15, 13.)
 CRLF = CR LF
 ctext = <any CHAR excluding "(", ; => may be folded
 ")", "\" & CR, & including
 linear-white-space>
 CTL = <any ASCII control ; ( 0- 37, 0.- 31.)
 character and DEL> ; ( 177, 127.)
 date = 1*2DIGIT month 2DIGIT ; day month year
 ; e.g. 20 Jun 82
 dates = orig-date ; Original
 [ resent-date ] ; Forwarded
 date-time = [ day "," ] date time ; dd mm yy
 ; hh:mm:ss zzz
 day = "Mon" / "Tue" / "Wed" / "Thu"
 / "Fri" / "Sat" / "Sun"
 delimiters = specials / linear-white-space / comment
 destination = "To" ":" 1#address ; Primary
 / "Resent-To" ":" 1#address
 / "cc" ":" 1#address ; Secondary
 / "Resent-cc" ":" 1#address
 / "bcc" ":" #address ; Blind carbon
 / "Resent-bcc" ":" #address
 DIGIT = <any ASCII decimal digit> ; ( 60- 71, 48.- 57.)
 domain = sub-domain *("." sub-domain)
 domain-literal = "[" *(dtext / quoted-pair) "]"
 domain-ref = atom ; symbolic reference
 dtext = <any CHAR excluding "[", ; => may be folded
 "]", "\" & CR, & including
 linear-white-space>
 extension-field =
 <Any field which is defined in a document
 published as a formal extension to this
 specification; none will have names beginning
 with the string "X-">
 August 13, 1982 - 44 - RFC #822
 Standard for ARPA Internet Text Messages
 field = field-name ":" [ field-body ] CRLF
 fields = dates ; Creation time,
 source ; author id & one
 1*destination ; address required
 *optional-field ; others optional
 field-body = field-body-contents
 [CRLF LWSP-char field-body]
 field-body-contents =
 <the ASCII characters making up the field-body, as
 defined in the following sections, and consisting
 of combinations of atom, quoted-string, and
 specials tokens, or else consisting of texts>
 field-name = 1*<any CHAR, excluding CTLs, SPACE, and ":">
 group = phrase ":" [#mailbox] ";"
 hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT]
 ; 00:00:00 - 23:59:59
 HTAB = <ASCII HT, horizontal-tab> ; ( 11, 9.)
 LF = <ASCII LF, linefeed> ; ( 12, 10.)
 linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE
 ; CRLF => folding
 local-part = word *("." word) ; uninterpreted
 ; case-preserved
 LWSP-char = SPACE / HTAB ; semantics = SPACE
 mailbox = addr-spec ; simple address
 / phrase route-addr ; name & addr-spec
 message = fields *( CRLF *text ) ; Everything after
 ; first null line
 ; is message body
 month = "Jan" / "Feb" / "Mar" / "Apr"
 / "May" / "Jun" / "Jul" / "Aug"
 / "Sep" / "Oct" / "Nov" / "Dec"
 msg-id = "<" addr-spec ">" ; Unique message id
 optional-field =
 / "Message-ID" ":" msg-id
 / "Resent-Message-ID" ":" msg-id
 / "In-Reply-To" ":" *(phrase / msg-id)
 / "References" ":" *(phrase / msg-id)
 / "Keywords" ":" #phrase
 / "Subject" ":" *text
 / "Comments" ":" *text
 / "Encrypted" ":" 1#2word
 / extension-field ; To be defined
 / user-defined-field ; May be pre-empted
 orig-date = "Date" ":" date-time
 originator = authentic ; authenticated addr
 [ "Reply-To" ":" 1#address] )
 phrase = 1*word ; Sequence of words
 August 13, 1982 - 45 - RFC #822
 Standard for ARPA Internet Text Messages
 qtext = <any CHAR excepting <">, ; => may be folded
 "\" & CR, and including
 linear-white-space>
 quoted-pair = "\" CHAR ; may quote any char
 quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or
 ; quoted chars.
 received = "Received" ":" ; one per relay
 ["from" domain] ; sending host
 ["by" domain] ; receiving host
 ["via" atom] ; physical path
 *("with" atom) ; link/mail protocol
 ["id" msg-id] ; receiver msg id
 ["for" addr-spec] ; initial form
 ";" date-time ; time received
 resent = resent-authentic
 [ "Resent-Reply-To" ":" 1#address] )
 resent-authentic =
 = "Resent-From" ":" mailbox
 / ( "Resent-Sender" ":" mailbox
 "Resent-From" ":" 1#mailbox )
 resent-date = "Resent-Date" ":" date-time
 return = "Return-path" ":" route-addr ; return address
 route = 1#("@" domain) ":" ; path-relative
 route-addr = "<" [route] addr-spec ">"
 source = [ trace ] ; net traversals
 originator ; original mail
 [ resent ] ; forwarded
 SPACE = <ASCII SP, space> ; ( 40, 32.)
 specials = "(" / ")" / "<" / ">" / "@" ; Must be in quoted-
 / "," / ";" / ":" / "\" / <"> ; string, to use
 / "." / "[" / "]" ; within a word.
 sub-domain = domain-ref / domain-literal
 text = <any CHAR, including bare ; => atoms, specials,
 CR & bare LF, but NOT ; comments and
 including CRLF> ; quoted-strings are
 ; NOT recognized.
 time = hour zone ; ANSI and Military
 trace = return ; path to sender
 1*received ; receipt tags
 user-defined-field =
 <Any field which has not been defined
 in this specification or published as an
 extension to this specification; names for
 such fields must be unique and may be
 pre-empted by published extensions>
 word = atom / quoted-string
 August 13, 1982 - 46 - RFC #822
 Standard for ARPA Internet Text Messages
 zone = "UT" / "GMT" ; Universal Time
 ; North American : UT
 / "EST" / "EDT" ; Eastern: - 5/ - 4
 / "CST" / "CDT" ; Central: - 6/ - 5
 / "MST" / "MDT" ; Mountain: - 7/ - 6
 / "PST" / "PDT" ; Pacific: - 8/ - 7
 / 1ALPHA ; Military: Z = UT;
 <"> = <ASCII quote mark> ; ( 42, 34.)
 August 13, 1982 - 47 - RFC #822