Outlook to Exchange Communication, which port?

Question

When outlook 2003 is setup with an Exchange 2003 server, within an internal network, and with 'Microsoft Exchange Server' as the 'Server Type', what port(s) are used?

Also, if it is a bunch of ports but it can be bound to specific port on the server side, where would I check if this had been done?

Solution

There is an initial communication from the client (on an ephemeral port) to the server's TCP port 135. The server's RPC endpoint mapper establishes a random port on the server and sends that to the client and then the client connects to that random port.

Here's an article from Microsoft that talks about what you'd need to do to establish static ports on the server: http://support.microsoft.com/kb/270836

If you want to quickly see if the server has this configured, go have a look at HKEY_LOCAL_MACHINE\System\CurrentContolSet\Services\MSExchangeIS\ParametersSystem and look for a value called "TCP/IP Port". (That's only one of the places where it would need to be set. The article can tell you the rest.)

(If you're looking for this to forward Outlook-to-Exchange communication across a firewall for a large number of clients think about using RPC-over-HTTP(S) (also known as "Outlook Anywhere") in lieu of making this change. If not, forget that I said anything...)