I am running a 550VPN firewall at an external IP address of x.x.x.2 (internal 192.168.2.1). My company's domain name is mycompany.com, with an MX record x.x.x.113. Reverse DNS points back to mail.mycompany.com. I then route ports 110 and 25 from x.x.x.113 to our mail server running on 192.168.2.123 This works fine in most cases, but we seem to be having mail rejected from mail.bellsouth.net and mail.aol.com, and I suspect it may be a DNS issue. The bounces from mail.bellsouth.net send a 452 error "Message rejected", which usually indicates a lack of storage, but I've checked and that's not the case. The AOL bounces send a 554 error. So I suspect these errors are bogus. Now, my question to you. If you examine the header on this message it says something like " Received: from pdsvr5 ([x.x.x.2])", which is the 550VPN. pdsvr5 is the netbios name of our mail server setting at 192.168.2.123. Would it make more sense to change the MX record to x.x.x.2? Do you think this could have anything to do with the AOL and BS bounces?