Help! Looking for a new Email program!

At my workplace we are using a G5 iMac running OSX version 10.3.9. We have been using Outlook Express 5 (5.0.6) for our email, which runs in Classic mode. However, it often crashes or has other problems and we would like to switch to something more reliable - and newer.

Are there any similar email programs that will run in our version of OSX without using Classic?

Any suggestions or advice would be most welcome.

THunderbird, open source and free

You can download version 2 here (version 3 only works with 10.4 Tiger and above)

Thunderbird 2.0.0.18 software download - Mac OS X - VersionTracker