Excellent E-mail client from the makers of Firefox

Thunderbird

Thunderbird 1.5.0.7 DownloadThunderbird 1.5.0.7 Date added: July, 30th 2006 - (Open Source)

What's new in this version:

MFSA 2006-64 Crashes with evidence of memory corruption (rv:1.8.0.7)
MFSA 2006-63 JavaScript execution in mail via XBL
MFSA 2006-60 RSA Signature Forgery
MFSA 2006-59 Concurrency-related vulnerability
MFSA 2006-58 Auto-Update compromise through DNS and SSL spoofing
MFSA 2006-57 JavaScript Regular Expression Heap Corruption