I've found that every time I update my Plesk 11 server, I can no longer send or receive email. I was able to find the following messages in my maillogs.
postfix/smtpd: connect from unknown[127.0.0.1] postfix/smtpd: fatal: host/service localhost/12768 not found: Name or service not known
The solution is actually very simple. Open your Postfix/Main.cf file
Now search for the word “milter” and comment those lines out.
#smtpd_milters = inet:localhost:12768 #non_smtpd_milters = inet:localhost:12768
service postfix restart