What is Return-Path?

The Return-Path is the address where bounces and other email feedback are sent. It is specified by the Return-Path header in an email. For example, the default Return-Path for emails sent through Postmark is:

Return-Path: <pm_bounces@pm.mtasv.net>

It is also described as:

• bounce address
• reverse path
• envelope from
• MAIL FROM

Why set a custom Return-Path?

DMARC requires the domains in the Return-Path and From headers to match in order for the SPF check to pass. Many email providers will set the Return-Path for you, so it’s common for the Return-Path and From domains not to match and therefore DMARC will not be aligned.

Note that DMARC only requires either SPF or DKIM domains to pass and align with your From domain, not both. However, having both SPF and DKIM passing and aligning helps combat forwarding/routing that may break authentication en route to the final recipient, which is out of the sender's control.