I'm having a problem getting emails to bounce to a specific email address, different to the From address.

A particular client requires that we send emails from a specific email address (call it [email protected]). Our Exchange admins have created an account on the Exchange box so that we can log in and send from that address. Our Exchange server is spoofing that address / domain. This works fine.

Unfortunately the emails sent from [email protected] are not bouncing back to us. They are presumably bouncing back to the contact account at clientcompany.com (which may or may not exist).

I've inserted a header [email protected] with the assumption that this field determines where bouncebacks are sent. Other documents indicate that this field should never be populated by the originating SMTP system. Other websites again talk about a field called Errors-To which is apparently non-standard.

So - which field is the correct one, and what does it depend on?
Any ideas why my Return-Path is not working?

I'd really like to get Exchange to correctly bounce a message addressed to an invalid server!

update:

Continuing to dig, and my Return-Path work was only adding an extended property at the end of the header block, but Exchange appears to be still adding its own Return-Path value at the top.

Delivered-To: [email protected] 
Received: by 1.1.1.1 with SMTP ... 
Return-Path: <[email protected]> 
Received: from ... ... 
...
Subject: Test 
Message-ID: ... 
Return-Path: [email protected]

According to the Microsoft.com, I cannot set the Return-Path as it is determined by the MAIL FROM - which seems consistent with what I've previously read. But now I'm stuck - how do I change this MAIL FROM value programmatically within Exchange 2007?