i dont know but hey you wanna be pen pals? when was the last time you did that? that would be cool huh?
i used to be a seamonkey user, loving it because it bundled web and email in the same suite but it was always three step behind firefox in devel so i switched to the couple firefox-thunderbird, eventually. i am not faithful to firefox (i also use chromium, opera for browsing), but Thunderbird is THE email client to me. if i have to make a choice and choose another client, i switch to Kmail, the default client with kubuntu linux/KDE . thunderbird is powerful and stable.
I used to be a Thunderbird fan, then they updated it and it never would work properly for me after that...couldn't work out why. I switched to Sylpheed untill such a time as Thunderbird sorted itself out, then found I liked it so much that I've stuck to it ever since. A bit basic maybe, but it does the job for me.
i just use plain old G-Mail, i have a gmail button on my bookmarks toolbar which works just fine for quick access instead of using an extra application like outlook or thunderbird to view my mail, I used to use thunderbird back when i had XP because it showed if i had new mail on the log on screen though im sure any email client done that on XP but thunderbird served me well.