Here's the seutp. I have two machines:
192.168.X.100 web server
192.168.X.101 email server

The machines are behind a proxy that forwards port 80 traffic to 192.168.X.100 and 110, 143 traffic to 192.168X.101. Makes sense right?

But now I want to setup a webmailer. The problem is webmail.mydomain.com would come in over port 80 and automatically get forwarded to 192.168.X.100.

How do I set it up so webmail.mydomain.com goes to my e-mail server at 192.168.X.101, while the rest of the port 80 traffic goes to my web server?

Thanks.

How many real-IP's have you got on your proxy server? If you want two distinct servers listening on the same port, you need two IP's.

Alternatively, you could put the webmail software on the webserver and set it up as a VirtualHost and then just configure the webmail software to connect to the mail servers local IP.

Thanks for the reply.
In case anyone else ever wants a setup like this, here's what I did to get it working:

The email server's apache now listens on port 8080.

webmail.mydomain.com on my web server now redirects traffic to webmail.mydomain.com:8080. I just used javascript in the webmail.mydomain.com's index page to redirect traffic, but it could've been done in the httpd.conf file.

The proxy server has been configured to direct port 8080 traffic to 192.168.X.101 instead of .100.

I don't know why I didn't just think of that before.

I have basically the same setup as msound and that's what I did. Squirrelmail runs on my webserver and retrieves the mail from my mailserver via local (NATed) IP address. It works seamlessly and flawlessly.

If you had a separate public IP for your two servers, you could also set up DNS so that webmail.yourdomain.com resolves to your mailserver's IP address, but it sounds like you only have one IP address, correct?