What is a Return-Path? (Envelope Sender / MAIL FROM)
The return-path, also called the envelope sender or MAIL FROM address, is the address given in the SMTP envelope when a message is sent — separate from the visible From: header — which receives bounce notifications and is the domain SPF checks.
Two senders on every email
Every email carries two sender addresses. The one people see is the From: header in the message itself. The other is the envelope sender, given in the SMTP MAIL FROM command before the message body is sent (RFC 5321). The envelope sender is where the receiving system sends bounce notifications, and when the message is finally delivered the receiving server records it in a Return-Path: header at the top of the message. That is why the three names — return-path, envelope sender and MAIL FROM — refer to the same address.
Why it matters for SPF and DMARC
SPF checks the domain of the envelope sender, not the visible From: domain. If your provider uses its own domain as the return-path, SPF passes for their domain, and DMARC cannot count that pass for yours because the domains do not align. Using a return-path on your own domain — typically a subdomain such as bounce.yourdomain.com — lets SPF align under DMARC’s default relaxed alignment, which gives you a second path to a DMARC pass alongside DKIM.
How a custom return-path is set up
The usual pattern is a CNAME from a subdomain of yours to a host your sending provider controls. The provider’s host carries the SPF record and MX that receive bounces, so you never have to maintain those yourself. PostStack asks for bounce.<your-domain> when you add a domain, and uses it as the envelope sender once the record verifies.
Bounce handling and VERP
Because bounces go to the return-path, it is also how a sender learns which recipient failed. Many platforms encode a per-message identifier into the local part of the envelope address (variable envelope return path, or VERP), so an asynchronous bounce can be matched to the exact message and recipient even when the bounce itself is badly formatted.
Frequently asked questions
Is the return-path the same as the From address?
No. The From: header is what the recipient sees. The return-path is the envelope sender given in the SMTP MAIL FROM command; it is where bounces go and it is usually set by your sending platform. They can be on the same domain, but often the return-path is a subdomain such as bounce.yourdomain.com.
Why does the return-path matter for DMARC?
SPF authenticates the return-path domain, not the From: domain. DMARC only counts an SPF pass if the return-path domain aligns with the From: domain. If your provider uses its own domain as the return-path, SPF cannot help you pass DMARC and you rely on DKIM alone.
How do I set a custom return-path?
Most providers ask for a CNAME from a subdomain of yours (for example bounce.yourdomain.com) to a host they control. Their host carries the SPF record and the MX that receives bounces. Once the CNAME verifies, the provider uses your subdomain as the envelope sender.