Milter is an add-on to an SMTP server like postfix. It enables a SMTP server to use external tools like SpamAssasin, Drweb, Kaspersky etc to scan emails.
Usually milter service is managed via the startup script /etc/init.d/pc-remote
Milter is running on port 12768 and bound to “0.0.0.0:*”
-bash-4.1# netstat -alpn | grep 12768
tcp 0 0 127.0.0.1:12768 0.0.0.0:* LISTEN 7216/psa-pc-remote
If milter service fails postfix wont be able to connect to port 12768 and it will stop email processing.
If milter service mail fails, you will see the following error in log & mail delivery.
postfix/smtpd: warning: connect to Milter service inet:localhost:12768: Connection refused
postfix/smtpd: NOQUEUE: milter-reject: CONNECT from unknown[192.168.52.36]: 451 4.7.1 Service unavailable - try again later; proto=SMTP
Milter can fail due to different reasons due to bugs in milter, processing of malformatted mail, large number of open files etc.
If you face issues due to frequent milter crash, the following solution may help.
Run following commands
chmod -v 755 /root/scripts/watch-milter.sh
Add following cron.
* * * * * /root/scripts/watch-milter.sh
1. Make sure that /etc/init.d/pc-remote service exists & it manages milter
2. Make sure that nc(netcat) is installed & /usr/bin/nc is availale. Else, please install it using "yum install nc"
3. This script is optimised for plesk servers & it assume that /usr/local/psa/var/log/maillog is the mail log
For more information regarding Milter crash, contact our specialised team at www.bytehouse.co.uk/contact for more assistance.