I just discovered this nasty bug. It cost me 5 days of outgoing email. Mozilla pretended to send the outgoing messages when, in fact, they were never sent. Although the situations where this might occur are probably relatively rare, the severe consequences of this bug made me want to post this warning.
When this bug happens to you there is no way to know that something wrong has occurred. There is no indication that something has failed until all of your contacts start asking why you haven't emailed them in a few days or weeks. Even then, you might not ever be able to know what is happening.
