Inbox file growing up

Hi,

First thank you, yours apps changed mylife, I just have a probleme with thunderbird,
when I delete mail in the application, it's not realy done in the "inbox" file, it's the same for "sent", I realized that because, I deleted a lot of mail and the "inbox" files of each account was still as big as before, full of rubish, especialy the attached files comming from spams, with virus (not active, but anyway).

I have to remove them manually with a text editor, wath could be the probleme?

Thank you again for your contribution.

PS : -when the "Portable Apps" will be able to run linux.
-Do you think about a portable "aMSN" and portable "Flock".