Ok, here's the scenario; â€¢ Our website (uscomputergroup.com) is accessible from the internet via the FQDN or the IP of 18.104.22.168 and is properly registered with our registrar with ns1.uscomputergroup.com and ns2.uscomputergroup.com as the name servers. â€¢ The name servers are registered as 22.214.171.124 and there are proper DNS A record entries for ns1 and ns2 at the domain. â€¢ We have a SonicFirewall handling traffic on this IP address (126.96.36.199) and all neccessary web traffic is being forwarded to a DMZ (10.X.X.X) where the Plesk server resides. â€¢ The network interface of the Plesk server has an IP address of 10.X.X.X â€¢ uscomputergroup.com is being physically hosted by Plesk on this IP but all DNS entries resolve to the public IP address (188.8.131.52) as required to be accessible from the internet. â€¢ checkdns.net successfully resolves all connection attempts including e-mail for uscomputergroup.com. â€¢ All of the POP e-mail boxes are working properly and we can send/receive e-mail to and from anywhere. Here's the problem; 1. When running the mail() function in PHP, sending an e-mail to firstname.lastname@example.org results in the following error; Is this because DNS resolves the domain (uscomputergroup.com) to the public IP address (184.108.40.206) and therefore assumes that it is "not local" since the physical IP address of the server is actually 10.X.X.X? 2. When creating a domain in Plesk, the default DNS entries are created using the physical IP on which it is hosted (10.X.X.X). However, these entries must resolve to the public IP address (220.127.116.11) in order to be accessible from the internet. Therefore, we must either; A. Manually input each DNS entry with the correct public IP address for the domain. B. Change the server default DNS entries to the public static IP address. Solution A. is not ideal for clients as this forces clients to manually edit thier DNS entries! Solution B. is not ideal as this forces all sites to use the same public IP address and does not allow a domain to have a dedicated IP address! If anyone has any ideas as how to resolve these issues, please respond and/or contact me. Thanks for your time and help!