Ubuntu :: Corrupt Version Of Thunderbird?

I'm running Xubuntu 10.4 and TB 3.0.6 from the repository, and the damndest thing has happened. Thunderbird was working, and then it stopped sending email -- literally from one email to the next. In fact, I didn't even notice it for three hours.

I never got an error message or a timeout or any of the typical problems; rather, I typed the email, hit send, and then it vanished from the screen. I don't get a progress bar on the bottom or a sent message line, and the message doesn't go into the sent folder. I can receive email, and my Internet connection is working.

I tried all the usual stuff -- checking the settings (which I haven't messed with), deleting each of my accounts and putting them back, looking for rogue extensions (again, I didn't add any between the time it worked and it didn't), and uninstalling, purging, reinstalling, etc. I even ran a virus scan.

But it gets weirder. I installed Evolution, and it works fine. And so does Spicebird, which is basically Thunderbird in prettier clothes. So the problem appears to be with the copy of Thunderbird that I have installed, since I haven't heard of anyone else having this problem.

Any thoughts? If this was Windows, I would assume that the software was corrupted or missing a ddl (or whatever), but I've never seen this happen on a Linux system.