According to
http://texturizer.net/thunderbird/faq.html#q2.8 it says,
Is Thunderbird susceptible to e-mail viruses?
Thunderbird will not allow a virus or worm to execute automatically. You can see what attachments have been sent to you without a virus being able to execute, and you would have to save a file to your system and deliberately run it before it could cause any harm.
JavaScript is switched off by default for mail and news, so an e-mail cannot run script code just by being opened.
As with any mail program, take proper caution before running any file that you receive in e-mail. Appropriate anti-virus software should also help keep you safer.
Your mail files are inside your profile (see the Profile Folder), in the Mail and (if you use IMAP) ImapMail folders. Each mail folder (Inbox, Sent, etc.) is stored as two files ? one with no extension (e.g. INBOX), which is the mail file itself (in "mbox" format), and one with an .msf extension (e.g. INBOX.msf), which is the index (Mail Summary File) to the mail file. Tell the other program to import mail from the file with no extension.
If you want to transfer a mail file to another Mozilla profile or another installation of Mozilla, simply put the mail file into the other installation's Mail folder.
Does that help you?