Mailroom: Infinite cycle when error mail is rejected
My mailroom instance received delivery failure notice and then it replied, that it cannot be processed. Then my relay server replied that the reply cannot be delivered. Then mailroom replied it cannot be processed. Then relay server replied it cannot be delivered. And so on... the servers played ping-pong with e-mails for weeks.
Quick workaround: I've set up filter to redirect mail without subaddress (the plus part) to root instead of delivering it to mailroom.
Mailroom is missing a check whether the mail is really a regular e-mail to be processed and not delivery failure notice or something like that.