I also opened a JIRA-issue on this (JBMAIL-24).
Currently, when mail-delivery fails, mail end in the DLQ, where it just sits and rots.
For 5xx style errors, mails should be handled back to the sending user informing him of the failure.
For 4xx style error, JBMails should try to redeliver a few times (with expoential backoff) and then in case of constant failure be handled back to the sender. There should be the possibility to inform the user after some time that the mail is deferred.
For the 5xx a task should e.g. check every minute the DLQ, take failed mail off it, atach a "failed mail " message and send it to the originating user.
For 4xx mails, I am not sure if they stay on the "outgoing" queue or what happens.
thats odd I get bounce messages.... KAbir are you watching? You worked on this... I think you wrote that code.