I have a separate apache 2 web server and a separate zimbra server setup in mixed mode.

My router port forwards port 80 to my web server and port 443 to the zimbra server. What I need to do is to forward port 80 traffic intended for mail.xxxx.com to the zimbra server whose host is mail. I want www.xxxx.com and all other web pages to remain in the apache 2 server.

I'm sure this is fairly simple and has been dealt with before, but I don't know what it's called and don't know what to search for. I've searched for virtual hosts, but everything I've found deals with setting up apache and zimbra on the same machine.