Rather than just download Thunderbird, you can always install something a little more interesting that will a) provide hours of fun setting up and configuring so that it works exactly the way you want it to, and b) will free you of the rodent…

• Mutt - a small but very powerful text-based mail client for Unix operating systems. Eminently extensible and configurable. mutt + imap + gmail ftw!
• Alpine - based on the Pine® Message System. Not as intimidating for the novice as mutt…
• Sup - a console-based email client for people with a lot of email. “The goal of Sup is to become the email client of choice for nerds everywhere”
• Notmuch - an answer to Sup. Still in the early stages of development, there are two user interfaces available for it, one for vim and one for those poor benighted souls still using emacs…
• Cone - a screen-oriented E-mail/News reader and writer. Cone contains an experimental implementation of a new remote mail access protocol, SMAP