modifying return-path

[garwain]

I've been working at developing a webmail site that handles several virtual domains, and after reviewing code for the last 3 hour I'm guessing it's postfix that's adding the Return-Path header line?

Is there any simple way I modify this line? I would like it to display the domain that the user is sending from instead of the server's primary domain name.


Any ideas/suggestions are appreciated.
Thanks