I have been meaning to try it. I don't know if I will switch over to it or not. I have 4-5 years of emails archived on my hard drive using outlook.

Thunderbird is supposed to be more secure than Outlook / Outlook Express.
I don't know if that's true or not, because if you know how to properly secure O/OE (and Windows in general) then there really isn't any worries.
Set O/OE to use the Trusted (restrictive) access, not to show HTML (text only), and not to allow execution of attachments.
Someone sends me a "screensaver" with an EXE extension?
That's nice - I can save it to my HD or ignore it, since OE won't download the attachment until I tell it to.
Someone sends a "Web bug" 1 pixel tracker in an HTML formatted email?
That's nice - too bad I don't USE HTML email & that web bug never loaded, much less reported back to its master.
Someone sends the latest VB virus?
(Snickers) Too bad I have ALL scripts (VB, WSH, JS) set to open with Notepad instead. Your virus didn't do anything but display in my clipboard.

If it ain't broke, don't fix it. =)P

DO you realise you resurected a thread that is over 3 years old and had died?

Cormac, I sent him a PM to quit resurrecting the dead; lets hope he reads it.