What is a Return-Path address?
The Return-Path address (also called envelope-from or bounce address) is the technical address used by the sending server to identify the actual sender of a message at the SMTP protocol level.
It is not always visible to the end user, but it plays an essential role in email transport.
This is the address that receives:
delivery failure notifications (bounces),
and is used for certain anti-spam checks (SPF, DMARC, etc.).
Simplified example:
Return-Path: <bounces@example.com>
From: Marie Dupont <marie@example.com>
To: contact@company.com
Here, the email appears to come from “Marie Dupont”, but technically, it is bounces@example.com that is used by the sending server.
Diagram:
À quoi sert-elle concrètement ? -> What is it actually used for?
Identifying the real sending server (used for SPF).
Handling automatic replies (errors, full mailboxes, invalid addresses).
Allowing anti-spam or security systems to perform checks on an authentic and traceable address.
Official reference (RFC)
The management of the Return-Path field is defined in the following standard:
RFC 5321 – Simple Mail Transfer Protocol (SMTP)
Section 4.4. Trace Information
Direct link to the RFC (in English):
https://datatracker.ietf.org/doc/html/rfc5321#section-4.4