The envelope sender, also called MAIL FROM, bounce address or Return-Path, is the address a sending server announces in the SMTP conversation. Delivery errors are returned to it, and the receiving server evaluates SPF against its domain.
Why it matters
An email has two senders: the envelope sender, which is for machines, and the From header, which the person sees. They can differ legitimately, for example when a newsletter platform sends with its own bounce domain. When the receiver delivers the message it records the envelope sender in a Return-Path header. Because the two addresses can be different, DMARC adds a requirement that one of them match the From domain, called alignment.
Example
MAIL FROM:<bounce+123@mailer.vendor.net>
...
From: Example Shop <hello@example.com>The recipient sees hello@example.com, but SPF is checked against mailer.vendor.net, and bounces go to the vendor. To align for DMARC, the vendor can sign with DKIM using d=example.com or use a custom bounce domain such as bounce.example.com.
Common mistakes
- Checking SPF against the visible From domain instead of the MAIL FROM domain.
- Using a no-reply envelope address that is not monitored, so bounce data is lost.
- Assuming Return-Path and Reply-To are the same thing; see Reply-To.
Related
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