I have bugzilla 4.2.5 running on Ubuntu using postfix. Email from bugzilla is sent from email@example.com. (The real name is altered). The email is sent through Exchange server. Up until recently everything worked perfectly. A few days back mail stopped being delivered. Mailq on bugzilla shows "(host exchange.mydomain.com[xxx.xxx.xxx.xxx] said: 452 4.3.1 Insufficient system resources (in reply to MAIL FROM command))".
Restart of the Transport service and even rebooting exchange didn't help. Mailq -q, postfix -f didn't help. I did figured out, however, that when mail gets to exchange as firstname.lastname@example.org it is accepted.
Can somebody suggest what needs to be done either on bugzilla or on exchange in order to fix it?