You export them from the computer they are on now and import the in Thunderbird on your home computer. To export or import in Thunderbird you open the address book, click on tools then export or import. Thunderbird will use .ldif, comma separated or tab delimited files.

IMAP works such that what you do in the client is reflected to the server, and vice versa. That's the point of it vs. POP3. Any messages you want to retain on the GMail server, you can't delete them from the (IMAP) GMail account tree in Thunderbird. I *never* keep long-term copies of mail on a server. It's *my* mail, I want it archived to *my* computer. IMO there's too much risk of a hacker getting access by brute-force or a server-side security flaw. My computer is more secure, less likely to be hacked, and I can back up the data. I have messages in Thunderbird that date 10 years back. And archived data MUCH older from Outlook Express.

Hello Sue, I would think preferences or account settings or options would be under the tools section did you look there, open thunderbird and open the tools tab in the top of the email window. Also see if this link is helpful, Here is a link that might be useful: thunderbird Mail help

Post this on the computer forum, they are really quick to get you answers. They help me often with my computer woes.