If you don't have a dedicated router (linksys, cisco, etc) but a Linux server working as a router, you have to set up port-forwarding wit iptables. This way you can "publish" sereral services using just one public IP.
<YourPublicIP>:80 -----> <Server1>:80
<YourPublicIP>:110 -----> <Server1>:110
and so
You can take a look at this guides
http://www.howtoforge.com/nat-gatewa...tu-8.10-server
http://www.debian-administration.org/articles/73
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