Return-Path is the email header the receiving mail server inserts into a delivered message containing the envelope sender address (from the SMTP MAIL FROM command). Any bounce or non-delivery report is sent to this address, not to the address in the visible From: header.
Example
Return-Path: <bounces+abc123@mailer.example.com>
Received: from mail-server.example.com...
Authentication-Results: mx.receiver.com; spf=pass...
From: "Marketing Team" <marketing@example.com>
To: alice@receiver.com
Subject: Weekly digest
...Return-Path vs From
- Return-Path — envelope-level, where bounces go, what SPF authenticates
- From — display-level, what recipients see
These may be the same address or totally different addresses. Large-scale senders commonly set Return-Path: bounces+recipient-id@mailer.example.com for VERP (Variable Envelope Return Path) bounce processing.
Why Receivers Insert It
The SMTP protocol delivers the envelope sender only in the MAIL FROM command — not in the message body. Without the receiver adding Return-Path, the delivered .eml file wouldn’t record who to bounce to. RFC 5321 §4.4 mandates that receiving MTAs prepend Return-Path on final delivery.
Common Confusion
- If you see
Return-PathandFromdiffer — that’s normal, not spoofing - SPF checks
Return-Path(the envelope sender), notFrom - DMARC alignment requires both to match
Inspect Return-Path handling for any domain with the email authentication checker.
Related
Check the MAIL FROM glossary entry, the envelope sender entry, and read what an SPF record is.