Here is code to parse and decode all types of messages, including attachments. I've been using something like this for a while now, so it's pretty robust.
<?php
function getmsg($mbox, $mid) {
 // input $mbox = IMAP stream, $mid = message id
 // output all the following:
 global $charset, $htmlmsg, $plainmsg, $attachments;
 $htmlmsg = $plainmsg = $charset = '';
 $attachments = array();
 // HEADER
 $h = imap_header($mbox, $mid);
 // add code here to get date, from, to, cc, subject...
 // BODY
 $s = imap_fetchstructure($mbox, $mid);
 if (!$s->parts) // simple
 getpart($mbox, $mid, $s, 0); // pass 0 as part-number
 else { // multipart: cycle through each part
 foreach ($s->parts as $partno0=>$p)
 getpart($mbox, $mid, $p, $partno0+1);
 }
}
function getpart($mbox, $mid, $p, $partno) {
 // $partno = '1', '2', '2.1', '2.1.3', etc for multipart, 0 if simple
 global $htmlmsg, $plainmsg, $charset, $attachments;
 // DECODE DATA
 $data = ($partno)?
 imap_fetchbody($mbox,$mid,$partno): // multipart
 imap_body($mbox,$mid); // simple
 // Any part may be encoded, even plain text messages, so check everything.
 if ($p->encoding==4)
 $data = quoted_printable_decode($data);
 elseif ($p->encoding==3)
 $data = base64_decode($data);
 // PARAMETERS
 // get all parameters, like charset, filenames of attachments, etc.
 $params = array();
 if ($p->parameters)
 foreach ($p->parameters as $x)
 $params[strtolower($x->attribute)] = $x->value;
 if ($p->dparameters)
 foreach ($p->dparameters as $x)
 $params[strtolower($x->attribute)] = $x->value;
 // ATTACHMENT
 // Any part with a filename is an attachment,
 // so an attached text file (type 0) is not mistaken as the message.
 if ($params['filename'] || $params['name']) {
 // filename may be given as 'Filename' or 'Name' or both
 $filename = ($params['filename'])? $params['filename'] :
$params['name'];
 // filename may be encoded, so see imap_mime_header_decode()
 $attachments[$filename] = $data; // this is a problem if two files have same name
 }
 // TEXT
 if ($p->type==0 && $data) {
 // Messages may be split in different parts because of inline
attachments,
 // so append parts together with blank row.
 if (strtolower($p->subtype)=='plain')
 $plainmsg .= trim($data) ."\n\n";
 else
 $htmlmsg .= $data ."<br><br>";
 $charset = $params['charset']; // assume all parts are same charset
 }
 // EMBEDDED MESSAGE
 // Many bounce notifications embed the original message as type 2,
 // but AOL uses type 1 (multipart), which is not handled here.
 // There are no PHP functions to parse embedded messages,
 // so this just appends the raw source to the main message.
 elseif ($p->type==2 && $data) {
 $plainmsg .= $data."\n\n";
 }
 // SUBPART RECURSION
 if ($p->parts) {
 foreach ($p->parts as $partno0=>$p2)
 getpart($mbox, $mid, $p2, $partno.'.'.($partno0+1)); // 1.2, 1.2.1, etc.
 }
}
?>