I had started looking at bounce issues a while back but never completed the work. It turns out bounce emails are problematic and the PHPMailer code included with WordPress has deprecated support for it. I’ve made some minor changes that may help those trying to use the bounce email address capability.
I stress the “may” aspect of it because my own testing I have been unable to get it to work. I have not seen anything not working from the changes I’ve made but I have not received any bounce emails either. They simply seem to go in the bit bucket as far as I can tell.
Due to this unreliability I am recommending against using the bounce email address feature and have added a warning on the settings page advising as much which appears when a bounce address is set.
From looking at email headers this morning, I believe they are constructed properly. I have no idea when bounced messages are actually routed versus discarded and different email servers seem to do it differently.Email Users Beta (805 downloads)