Linux Gateway and POP3

[ald]

Hi.

I'm trying to setup a Linux computer as a gateway for Windows clients.  
I enabled masquerading and forwarding for the local network, and things 
work pretty well (people can web-browse, use AIM, ftp, so on), but they 
can't check their pop3 email accounts.  I have Roadrunner, and am using 
their off-site pop-server (pop-server.kc.rr.com:110).

I've picked up that for whatever reason that particular service isn't 
forwarded with everything else.  I'm curious about why that is, but more 
so on ways to fix it.  Are there any Linux apps that'll serve as 
gateways for pop3 transfers? 

~Adam Davis