Custom Return Path with Postmark

Front Lobby sends transactional emails via Postmark. Every week Postmark sends me an email with numbers of emails sent and delivered, which is nice.

That email also includes a list of deliverability recommendations - and for the longest time that list has contained “Set up a custom Return-Path for”. I figured it was time to do something about it.

Find your custom return-path

In Postmark under your “Sender Signatures” you’ll find a list of the domains you’ve added to Postmark. If any of those are highlighted with “Return-Path Not Verified” in red text you should follow along here.

Under the domains DNS settings (still in Postmark) is a row with “Return-Path” and “Inactive”. By default, Postmark suggests you use pm-bounces as the return path. Unless you have special requirements, just use the that.

The row also shows us the value we need to add as a CNAME for whatever we chose as the return path above. In my case I had to add a CNAME record for with a value of

Verify the changes in Postmark

After adding the record in my DNS provider I can head back to Postmarks DNS Settings interface to click the “Verify” button. If everything is correct, you should see a green checkmark and a “Verified” message!

What is the return path?

When you send a transactional email via an ESP like Postmark, you’ll usually send from a recognizable email address like “” to ensure that your recipients recognize the sender and can reply to you.

However if an error occurs delivering your email the receiving server needs a place to deliver error reports and whatnot. Those error report emails should end up with your ESP so they can handle them, instead of cluttering up your inbox.

The email address that email servers send those errors to is the return path (or bounce accress or a number of other names). If you don’t do anything it’s going to be something like (I don’t know what the actual address for Postmark is), which is perfectly fine.

However, if you’ve set up DMARC for your domain (and you should have), recipient servers might start flagging your emails in the above - even though both SPF and DKIM pass!

Basically the recipients look at the domains from both the From address (ie and the bounce address (ie It then compares those domains to the ones you’ve authenticated via DKIM and SPF and if it doesn’t match the entire DMARC authentication fails and you risk your email not being delivered.