Sent Mail all marked Junk - Mail will not learn!

Hi,

I'm on OS 10.4.10 and using Mac Mail v 2.1.

Recently all my Sent Mails are being marked as Junk. I've manually gone through hundreds of my sent emails and marked them Not Junk, but it still happens consistently. Every Sent Mail is marked Junk, regardless of receiver.
The computer crashed a couple months ago (folder with question mark - scary) and I had to do a complete erase and then reinstall everything. This Sent Mail as Junk Mail started happening after that. Help!
Also on the subject of Junk, Mail sometimes marks real emails as Junk Mail and does not seem to learn when I manually mark it as not junk and move into my Inbox. Even when I send an email to myself, it goes into Junk.