Thunderbird does a few things that will immediately put your mind at ease:
Why are these things important? Scripts can carry executable files that can cause irreparable damage to your email as well as to your computer. If you save your email locally to your hard drive, there are scripts that can run on your computer that can erase your hard drivethus taking away all your saved mail in one fell swoop. Thunderbird puts you in control by not allowing these scripts to run by default.
Many spammers have now harnessed the power of remote content and are using it to harvest email addresses to propagate more spam. Thunderbird puts you in the driver's seat by allowing you to control who can send you messages and content.
Finally, fighting spam is an almost endless battle. Spammers can bring corporate mail servers to their knees and waste valuable resources. Even server-side spam filters can't catch every piece of spam. When trained, Thunderbird's junk mail controls helps keep your inbox spam-free.
Let's forge ahead and see some of these concepts in action. Pass the ham, and please hold the spam.