Redirect Ports to Internet Clients

[Pilot1]

We host a web and email server on one Windows 2000 Host. I host only Imap email (web mail) access outside our boundary router to the internet on port 3000. Of course the web server uses port 80 to serve up web pages. Is there a way to redirect web clients without having to have them specify

http://example.com:3000

to log on. Instead something like

http://mail.example.com.

I can change the Imap port to anything I desire. Any ideas??

Pilot1