Envelope sender
The address given in the SMTP MAIL FROM command, where bounces and delivery reports are sent; also called the return path or bounce address.
What it means
RFC 5321 calls it the reverse-path and RFC 5598 writes it RFC5321.MailFrom; providers say envelope from, return path or bounce address. The sending system sets it, not the person writing, and it often differs from the visible From address: platforms use an address on their own domain or on a subdomain of the sender's so that bounces come back to their processing. At final delivery it is recorded in the Return-Path header.
The envelope sender matters for authentication. SPF checks its domain, and for that SPF result to count toward DMARC the domain has to align with the From domain, which is why senders set up a custom bounce (return-path) domain under their own domain with their sending platform. An empty envelope sender, written <>, marks a bounce or other notification that must never itself be bounced.
Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 5321, section 2.3.1: Mail Objectsrfc-editor.org
- RFC 5598, section 4.1.4: Identity References in a Messagerfc-editor.org
- RFC 7208, section 2.4: The "MAIL FROM" Identityrfc-editor.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes