in MailQueueImpl, you have something like this:

if (sending) return;
sending = true;
while (items in the q) {
try

catch (MailException me)

}

sending = false;

if an unchecked exception is ever thrown while sending a message, the queue
will never reset "sending", and as such will cease sending mail.

We are currently seeing JIRA stop sending mail under some circumstances. it seems to be related to sending to invalid addresses, although I haven't been able to reproduce the problem yet. also, I have no reason to think that the bug described above is the cause of our problem. was just something I ran across while looking for the source of our problem.