Greetingz!
Sounds like you're looking for a good email
client for Linux. There's quite a few;
Mozilla ThunderBird
Mozilla SeaMonkey
Evolution (Typically comes with GNOME)
Kmail (Typically comes with KDE)
Balsa (An email client for GNOME)
Every one of these email clients can be configured to read-in email from a POP3 server, and send out via an SMTP server (such as those for gmail).
However, if you're looking to
serve email to your fellow employees (as in, to replace your gmail accounts), then you might want to look at the following;
Guide for Ubuntu+PostFix (with Anti-Virus & Anti-SPAM)
Guide for RHEL5/CentOS5+ (with extras such as Anti-Virus)