From header
The header field naming the message's author: the address and display name a reader sees as the sender, and the domain DMARC protects.
What it means
RFC 5322 makes From one of the two required fields and defines it as the author's mailbox, optionally with a display name: From: Ana Silva <ana@example.com>. It may legally list several authors, in which case a Sender field is required, but receivers dislike it: Gmail rejects messages with more than one address in From, Google's guidelines ask for exactly one, and Microsoft rejects several From addresses without a Sender (550 5.1.20).
The From domain is the identity readers trust, so it is the one DMARC protects: a message passes DMARC only if SPF or DKIM authenticates a domain aligned with it. The From address can differ from the envelope sender and from the Sender and Reply-To fields, and for mail sent through platforms it usually differs from the envelope sender.
Example
From: Ana Silva <ana@example.com>Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5322, section 3.6.2: Originator Fieldsrfc-editor.org
- RFC 9989: Domain-Based Message Authentication, Reporting, and Conformance (DMARC)rfc-editor.org
- Google, Gmail Help: Email sender guidelinessupport.google.com
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
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