Emails are not delivered occasionally: warning: read TCP map reply from 127.0.0.1:12346: unexpected EOF (Connection timed out)

Symptoms

Mail delivery does not work periodically. The following messages can be found in /var/log/maillog:

CONFIG_TEXT: Jun 13 12:05:14 hostname postfix/smtpd[2177845]: warning: read TCP map reply from 127.0.0.1:12346: unexpected EOF (Connection timed out)
Jun 13 12:06:56 hostname postfix/smtpd[2177845]: warning: read TCP map reply from 127.0.0.1:12346: unexpected EOF (Connection timed out)
Jun 13 12:06:56 hostname postfix/smtpd[2177845]: warning: tcp:127.0.0.1:12346 lookup error for "[email protected]"
Jun 13 12:06:56 hostname postfix/smtpd[2177845]: NOQUEUE: reject: RCPT from mailexample.com[203.0.113.2]: 451 4.3.0 <[email protected]>: Temporary lookup failure; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<mail.example.com>
Jun 13 12:06:56 hostname postfix/smtpd[2177845]: lost connection after DATA from mail.example.com[203.0.113.2]
Jun 13 12:06:56 hostname postfix/smtpd[2177845]: disconnect from mail.example.com[203.0.113.2]

Cause

Not clear. Temporary Postfix or SRS (Sender Rewriting Scheme) issue.

Resolution

1. Connect to the server via SSH;
2. Check the postfix-srs line in /etc/postfix/master.cf configuration file. The correct output should be as follows:

   # grep postfix-srs /etc/postfix/master.cf
   127.0.0.1:12346 inet n n n - - spawn user=popuser:popuser argv=/usr/lib/plesk-9.0/postfix-srs

   If it is different, correct it and restart Postfix:

   # cp -p /etc/postfix/master.cf{,.bak}
   # sed -i '/postfix-srs/c\127.0.0.1:12346 inet n n n - - spawn user=popuser:popuser argv=\/usr\/lib\/plesk-9.0\/postfix-srs' /etc/postfix/master.cf
   # service postfix restart

3. If the steps above do not help or the configuration is correct, try to temporary disable and then re-enable SRS back according to the following article: How to turn off Sender Rewriting Scheme support?