IMAP Envelope

Apr 20, 2016



FETCH Response

A parenthesized list that describes the envelope structure of a message. This is computed by the server by parsing the [RFC-2822] 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-2822] 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.

If the Date, Subject, In-Reply-To, and Message-ID header lines are absent in the [RFC-2822] header, the corresponding member of the envelope is NIL; if these header lines are present but empty the corresponding member of the envelope is the empty string.

Note: some servers may return a NIL envelope member in the “present but empty” case. Clients SHOULD treat NIL and empty string as identical.

Note: [RFC-2822] requires that all messages have a valid Date header. Therefore, the date member in the envelope can not be NIL or the empty string.

Note: [RFC-2822] requires that the In-Reply-To and Message-ID headers, if present, have non-empty content. Therefore, the in-reply-to and message-id members in the envelope can not be the empty string.

If the From, To, cc, and bcc header lines are absent in the [RFC-2822] header, or are present but empty, the corresponding member of the envelope is NIL.

If the Sender or Reply-To lines are absent in the [RFC-2822] header, or are present but empty, the server sets the corresponding member of the envelope to be the same value as the from member (the client is not expected to know to do this).

Note: [RFC-2822] requires that all messages have a valid From header. Therefore, the from, sender, and reply-to members in the envelope can not be NIL.

References

RFC-3501 IMAPv4 - FETCH Response