I installed Exchange Server 2007 on a server with MS Server 2008 R2 Std. It is connected to the Internet through WAN 1 which comes through a Zyxel Zywall USG 100 firewall. The domain is through Godaddy who is also providing the current IMAP email service. I added MX & A records in Godaddy to point it to the server using the static public IP address. I used MXToolbox to test the connection. It shows the server at mail."mydomain".com & the public IP address but fails the SMTP test because of no response on port 25. On the Exchange Management Console/Microsoft Exchange/Server Configuration/Hub Transport/Receive Connectors/Default "server name" the FQDN is mail."mydomain".com & under the network tab ports 25, 80 & 443 are available for all IP addresses to receive mail. Anonymous users are permitted under Permission Groups. I unchecked Exchange Server authentication under the Authentication tab to allow changing the FQDN. I have not modified any settings on the Windows or Zyxel firewalls because I read that SMTP was built in on the server & I assumed the ZyXel firewall would allow it by default since it already works with POP & IMAP. I also used Microsoft Remote Connectivity Analyzer using a test email address created in the server & had the same results.