Portable Thunderbird is the popular Mozilla Thunderbird email program packaged as a cross-platform portable app, so you can take your email, drafts, cache, newsgroups, and saved passwords with you. It works on both Macs and PCs.
How It Works
Cross-platform Portable Thunderbird works by using John Haller’s excellent Portable Thunderbird 1.5 on the Windows side of things, and a little script he made on the Mac side of things. The script basically changes your user profile every time you start Thunderbird so that it works on Mac and PC. The reason why is simple: as I am sure some of you have figured out, Windows Thunderbird profiles are not completely compatible with Mac Thunderbird, only certian files. So he made a script that keeps compatibility between Mac and PC, time consuming, I know, but it works.
Check it out at: http://www.theplaceforitall.com/portablethunderbird/
Also, check out: http://portableapps.com/