I have an Exchange 2007 SP3 CAS server with two network interfaces, one on an internal network and one in our DMZ. POP3 is enabled on both interfaces; when I telnet to port 110 on the DMZ interface I get the expected POP3 prompts, however when I telnet to port 110 on the internal interface I receive an SMPT prompt instead of the expected POP3 prompts. I have tried defining the POP3 service using the generic "Use all IP addresses available on this server" as well as individual entries for both interfaces. I get the same results either way. I did restart the POP3 service after making each configuration change. Windows Firewall is disabled on this server. Has anyone elsse run into this, or have any ideas for what is happening?

To confirm when you telnet to port 110 on the internal interface you're getting the SMTP 25 banner instead of the pop3 banner?James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

That's correct, and it does respond correctly to SMTP commands.

Below is a transcript of telnet sessions to both interfaces: Jeffs-MacBook-Pro:~ jeff$ telnet 192.168.9.172 110 Trying 192.168.9.172... Connected to ex-hub1.hkusa.com. Escape character is '^]'. 220 ex-hub1.hkusa.com Microsoft ESMTP MAIL Service ready at Mon, 10 Sep 2012 15:44:16 -0500 quit 221 2.0.0 Service closing transmission channel Connection closed by foreign host. Jeffs-MacBook-Pro:~ jeff$ telnet 192.168.14.172 110 Trying 192.168.14.172... Connected to ex-hub1.hkusa.com. Escape character is '^]'. +OK The Microsoft Exchange POP3 service is ready. user jeffgt +OK quit +OK Microsoft Exchange Server 2007 POP3 server signing off. Connection closed by foreign host.

When you're testing the internal interface, you're testing from a client that's internal to the Exchange server's internal interface correct? Just making sure your firewall is not doing some incorrect port mapping from 110 to 25. What about if you telnet locally on the exchange server to itself on the internal interface does the pop3 banner show up?James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

I have tested from a machine that is on the same vlan as the local interface as well as one that is not with the same results. Also testing from the CAS server itself yields the same behavior.

hi, Try to restart the pop3 service, then see if the issue is still occured. Similar thread:http://social.technet.microsoft.com/Forums/en-US/exchangesvrtransport/thread/badf34f8-419e-4c21-a9ae-64915e770c7d/ hope can help you thanksCastinLu TechNet Community Support

Thank you all for the input, I have finally figured out what was happening. The receive connector on the internal interface was enabled on port 110 as well as 25, allowing it to stomp on the POP3 service. Once I changed to config to allow for only port 25 and restarted the Transport service, I was able to accessPOP3 on the internal interface.