Incoming Queuing

MTA kicks off a fml process. It reads a message from STDIN.

The fml process reads a message once and write it onto the hard disk (write it into the incoming queue). After the queuing succeeded, the process starts to analyze a message. For this logic, the original mail is saved before main processing starts.

If the queuing fails, fml calls exit(EX_TEMPFAIL). In almost cases, exit(75). If MTA receives this exit code, MTA tries to deliver again later.

Mail::Delivery::Queue class processes the incoming queue. The queus is removed when the process ends.