Email Author Header Field
Internet mail defines the From: header field to indicate the author of the message's content and the Sender: field to indicate who initially handled the message on the author's behalf. The Sender: field is optional if it has the same information as the From: field. This was not a problem until development of stringent protections on use of the From: field. It has prompted Mediators, such as mailing lists, to modify the From: field to circumvent mail rejection caused by those protections. In effect, the From: field
Experimental, not a standard. Published to be tried rather than relied on. Implementations may legitimately disagree.
What it is
An Author header field, distinguishing who wrote a message from who sent it.
What it solves
DMARC alignment forces mailing lists to rewrite From:, which loses the original author.
What it means to operate
Experimental, so treat it as a direction rather than something to deploy. Worth knowing because it is one of the answers being explored for the From: rewriting that DMARC enforcement forces on lists.
Header analyser parses a real message and says what each header is claiming. Open header analyser
Normative requirements
Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from.
3 Author Header Field
- MUST NOT* If an Author: field already exists, a new one MUST NOT be created, and the existing one MUST NOT be modified.
- MAY* An author's MUA or MSA MAY create an Author: field, and its value MUST be identical to the value in the From: field.
- MAY* A Mediator MAY create an Author: field if one does not already exist, and this new field's value MUST be identical to the value of the From: field at the time the Mediator received the message (and before the Mediator causes any changes to the From: field).