Sorry in advance for the long post, but I want to make sure I include all relevant info. I've been using one of the webmail apps (UebiMiau) that comes with ISPConfig and it works just fine. However, I'm having two different problems with using the PHP mail() function on my websites at IP addresses which are different from the IP that ISPConfig runs on. These two problems may or may not be related to each other, so I'll describe them both here just in case. The first problem has to do with the way mail is handled when I do a simple test with the PHP mail() function. I run this script from one of my virtual sites (email addresses changed to protect against SPAM): Code: <?php $to = "[email protected][email protected][email protected] After running it, I always get new mail in my system mailbox (/var/mail/shaun ... not /var/mail/www-data). This is what it says: Code: From [email protected][email protected][email protected][email protected][email protected][email protected][email protected][email protected] My mail.log: Code: Aug 24 09:37:54 postfix/pickup: 48BE63588001: uid=33 from=<www-data> Aug 24 09:37:54 postfix/cleanup: 48BE63588001: message-id=<[email protected][email protected][email protected] As you can see from the above log output, the status is "sent", but I can't tell if it's bouncing back or if it's going directly into my system mailbox. I think I understand what's going on with my second problem, but I don't know how to fix it. One another site (at a different IP), I'm using HTML Mime Mail (http://www.phpguru.org/static/htmlMimeMail5.html) and I keep seeing messages in the www-data system user's mailbox that look like this: Code: <[email protected][email protected][email protected] I have 3 public IP's. One IP is for an e-commerce site which requires SSL, the other IP is for ISPConfig/my site, and the last IP is for virtual hosting of basic PHP-enabled web sites. I assume that webmail works because webmail sends from the ISPConfig IP and passes the DNS lookup test, but when mail is sent from PHP scripts running at a different IP, it fails the DNS lookup and bounces back. Does anyone know how I can fix this so the PHP mail() function works AND passes the host/DNS test?