I'm trying to configure the included POP3/SMTP services in Windows Server 2003 Standard Edition. The POP3 service is only receiving messages from accounts on the domain and from no place else.
I'm using Outlook to send and receive messages. I can send email from email@example.com to my GMail account just fine, but when I reply in GMail, it never hits the mailbox on the server, nor do I get any error messages. To troubleshoot it, I created a second user on the POP3, and using the same public connection (mail.mydomain.com) sent an email to firstname.lastname@example.org. It came through just fine.
Is there some type of blacklist/whitelist for the POP3 service that I'm not finding? It seems that might be the problem, as its clearly accepting email, but only letting through messages from its own domain.