Well i use outlook express, thunderbird, firefox with spam programs and all work with no problems what so ever. Your situation, the way it is explained and our limited access to see what is happening on your end, certainly isnt helping much. You have uninstaled avast now what 10 times or more. Avast isnt causing these problems, it just isnt feasable. I would at this point, and its my last educated guess for you, is to uninstal thunderbird, wipe out all registry entries. Then reinstal again, perhaps something is botched in the thunderbird program itself ( bad original exe--D/L fresh new version, not the one you have ). Thats all I have for you. Good luck.