I am currently hosting a few websites with ISPConfig and use Postfix simply to relay web generated emails (from web site contact forms) via smtp. I don't do any local mail hosting. This is working fine, however my problem is that when I inspect the headers of the emails generated from my sites they all contain "Return-Path:" and "Received:" from my own domain, rather than the domain from which the email originated. For example, say my main domain is www.site1.com but I am sending an email via a contact form at www.site2.com. If I look at the email header it looks like the email originates from site1.com when it should be originating from site2.com. In my main.cf I have myhostname set to site1.com. Don't know what this should be set to in an ISP environment. I am new to Postfix and have spent several hours trying to find a solution to my problem - Thanks for any pointers!
If you're using PHP's mail() function to send mails, you should set additional headers, as shown on http://de3.php.net/manual/en/function.mail.php
