MAIL FROM and Return-Path
Also called: envelope sender, reverse-path, Return-Path
MAIL FROM is the SMTP command that begins a mail transaction; its argument is the reverse-path, or envelope sender. At final delivery this is recorded in the Return-Path header, which is where non-delivery reports are sent.
In plain terms
The address the mail system uses for bounces. It is not the From: address your recipient sees, and it often should not be.
Why it matters for deliverability
SPF authenticates this address, not the visible From:. That single fact explains most SPF results that look wrong: the check passed or failed against an envelope domain nobody was looking at.
What to do about it
- Point Return-Path at a mailbox or endpoint you actually process bounces from.
- When checking SPF, check the envelope domain rather than the header From domain.
- Remember that a message can pass SPF on the envelope and still fail DMARC if that domain does not align with the visible From.
Source
RFC 5321 — Simple Mail Transfer Protocol
“The primary purpose of the Return-path is to designate the address to which messages indicating non-delivery or other mail system failures are to be sent.”
Checked 2026-08-29
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