Two suggestions: 1) Is some of the space being taken up with email attachments? Do you need to keep them? In particular, if you have sent messages with files attached, those files may be stored in the 'sent' folder, but also still on your computer in the original locations. 2) Do you ever compact your folders? You need to understand that when you delete a message from Thunderbird, it's not actually deleted from the mail folder, it's just hidden from view. So if you've had this installation for a long time, all the emails you have ever deleted may still be there: that might account for the fact that the profile is growing continually. Read more here: http://kb.mozillazine.org/Compacting_folders