MailFetcherService does not delete mail message if it is unable to forward the mail because of an exception

MailFetcherService does not delete mail message if it is unable to forward the mail because of an exception. We have seen on support.atlassian.com that a mail was being forwarded and the mail was larger than the mail service was willing to accept. This caused an exception to be generated but the mail was left in the box so it was processed over and over.

A further problem with this is that if the mail is being fetched is fetched via pop then you can still run into JRA-11046.