[cnagele]

Note: I run Postmark (http://postmarkapp.com) where we handle delivery and bounce processing for a huge volume of email.

It depends on how the emails are being sent. The typical approach is to set a "Return-Path:" header in your outbound messages. The email that this is set to will get NDRs from receiving mail servers. You can then collect these NDRs in a mailbox or Maildir in Postfix and process them as needed. The benefit of this is having a single place where all of the messages are stored, even when sending from many FROM addresses.

I'd recommend a commercial tool to do this unless you already have tens of thousands of NDRs to learn against. You'll find that every mail server and ISP has something slightly different and it's very difficult to process each message accurately all the time. One example of a commercial NDR processing tool is Boogie Tools:

http://www.boogietools.com/

To take this a bit further, if you are using a Return-Path header, just make sure you also setup the proper SPF and DKIM records in DNS for better deliverability. You may also want to read up on VERP.

http://en.wikipedia.org/wiki/Variable_envelope_return_path