I am trying to set up a POP3 server on Windows Server 2003. I installed the POP3 service and created a mailbox. I also opened port 110 on the Windows Firewall and my router. I use Zonomi DNS Hosting and have a domain for my IP address. In Mozilla Thunderbird, I set up an e-mail account for "testaccount@<mydomain>" (it isn't actually <mydomain>.us, that's just for security reasons). The SMTP server I a using is smtp.comcast.net 587 this works fine for sending e-mails from "testaccount@<mydomain>". My problem is it keeps saying "Sending of password did not succeed. Mail server <mydomain> responded: Logon Failure". I don't know how to fix this. Is there anything which could cause this problem? Maybe folder permissions on the server or MX records?