Configure POP and IMAP in Exchange 2007

In either case, you use the ProxyTargetPort switch with Set-IMAPSettings or Set-POPSettings. Specify a proxy target port of 0 to turn off proxy requests altogether, or specify the port number you want to use for proxy requests. In other words, if you want to block IMAP or POP users from connecting to an Exchange 2003 mailbox through an Exchange 2007 CAS, set the ProxyTargetPort value on the CAS to 0. Bear in mind that Exchange 2007 won't use SSL to proxy IMAP or POP traffic to an Exchange 2003 server; you need to use IPsec if you want to encrypt that traffic to protect against eavesdropping and tampering.

Provide Message Transport
Remember that POP and IMAP are both client protocols. They let clients retrieve and manage messages, but clients can't use them to send messages back to the outside world. For that, you still need SMTP. In previous versions of Exchange, you generally have to set up a separate SMTP virtual server or connector that allows relaying for authenticated users.

Many administrators pick their own random, non-standard port number for these services. However, the Internet Engineering Task Force (IETF) has established port 587 as the preferred port for secure SMTP connections for IMAP and POP clients, and Exchange 2007 provides a receive connector for these clients by default. You can still choose to let clients directly connect to your Edge Transport or Hub Transport servers by using SMTP port 25 (preferably with authentication), but using port 587 instead gives you better security because those connections are automatically protected with SSL and with authentication required.

Conclusion
Many early reviews of Exchange 2007 have complained about the fact that IMAP and POP settings can be managed only through the Exchange Management Shell. It's true that this is a regression in functionality from Exchange 2003, but it shouldn't be a major problem for two reasons. First, Exchange Management Shell commands that manage IMAP and POP are dead simple to use. Anyone who can use the standard Windows command line to run ipconfig should be able to manage Exchange Management Shell commands. Second, POP and IMAP servers typically require little configuration because Microsoft has specified a reasonably secure and useful set of defaults. (For more information about Exchange 2007 management, see "Introducing Windows PowerShell," August 2006, InstantDoc ID 50565 and "Coming Out of Your Shell," a Windows IT Pro Web-exclusive, InstantDoc ID 95715.)