Question : Keep Return-Path header in Postfix

We use Postfix to send emails from Java (Tomcat). We want to give each outgoing message a unique Return-Path header, so that our system automatically can register bounced email addresses.

For example, when I send an email to [email protected] I want to use a Return-Path as [email protected]domain.com. And when I send an email to [email protected] I want to use a Return-Path as 1235-oijdfoijdfj33@bounce.mydomain.com.

I set the unique Return-Path header in the email in Java, before passing it on to Postfix through an SMTP connection. I have logged the outgoing message, and it has the correct (unique) "Return-Path" address.

However, when the email arrives to the recipient the Return-Path is set as [email protected]. This is the email address used in From. It seems that Postfix automatically resets our custom Return-Path header with the From header.

I believe this is in line with the SMTP guidelines, when an SMTP server gateway sends an email it should reset the Return-Path header.

How can I configure Postfix so that it does NOT change the Return-Path header for my own emails?

Answer : Keep Return-Path header in Postfix

Return path is something that the MTA (in your case postfix) will always replace with whatever it received in the MAIL FROM: during the SMTP exchange, and not what the headers say.

So can you Java smtp api actually specify the from address (the "envelope from", not the "From:" header)?  Your trick is to put your code into the api in a way that makes it put that into MAIL FROM: during the smtp conversation.

The from in the mail headers aren't used (sometimes they are adjusted) by the MTA.

You might also try adding a X-Errors-To: and Reply-To: headers.  Some MTA's will use them.