Update to Internet Message Format to Allow Group Syntax in the "From:" and "Sender:" Header Fields
The Internet Message Format (RFC 5322) allows "group" syntax in some email header fields, such as "To:" and "CC:", but not in "From:" or "Sender:". This document updates RFC 5322 to relax that restriction, allowing group syntax in those latter fields, as well as in "Resent-From:" and "Resent-Sender:", in certain situations.
Normative requirements
Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from. 2 must, 6 should, 1 may.
2.1 Replacement of RFC 5322, Section 3.6.2. Originator Fields
- MUSTIf the from field contains more than one mailbox specification (including all mailboxes included in any groups), then the sender field, containing the field name "Sender" and a single address, MUST appear in the message.
- SHOULD NOTThe from field and the sender field SHOULD NOT use group syntax; rather, the from field SHOULD use only the mailbox-list syntax and the sender field SHOULD use only mailbox syntax (see RFC 6854, Section 3).
- MUST NOTIf the sender field uses group syntax, the group MUST NOT contain more than one mailbox.
- MAYIn either case, an optional reply-to field MAY also be included, which contains the field name "Reply-To" and a comma-separated list of one or more addresses.
- SHOULD NOTIf the originator of the message can be indicated by a single mailbox and the author and transmitter are identical, the "Sender:" field SHOULD NOT be used.
- SHOULDOtherwise, both fields SHOULD appear.
- SHOULDIn the absence of the "Reply-To:" field, replies SHOULD by default be sent to the mailbox(es) specified in the "From:" field unless otherwise specified by the person composing the reply.
- SHOULD NOTIn all cases, the "From:" field SHOULD NOT contain any mailbox that does not belong to the author(s) of the message.
3 Applicability Statement
- SHOULD NOTIn particular, user agents SHOULD NOT permit the use of groups in those fields in outgoing messages.