If I send an email and enter an incorrect SMTP password, the email is added to the "sent" folder, regardless of the failed send process. I think, either it should be added _after_ sending it successfully or deleted automatically if sending fails. Btw you should add v0.7 to Bugzilla, last version to select is 0.6 ;-)
For technical reasons (BURL), it is actually needed to save the mail before it gets submitted via SMTP. There's a standard for saving a message *and* indicating that it's still pending submission. We currently do not implement that (see bug 354394). (Added v0.7, thanks.)
Let's track this in the original bug. *** This bug has been marked as a duplicate of bug 354394 ***