Unable to start Postfix on Plesk server: not owned by postfix

Symptoms

• Unable to start Postfix without any error message:

  # /etc/init.d/postfix start

  Starting postfix: [FAILED]

• No logs appear in the /var/log/maillog and /var/log/messages files.

• Starting Postfix manually shows the following warnings and errors:

  # /usr/sbin/postfix start

  postfix/postfix-script: warning: not owned by postfix: /var/lib/postfix/./prng_exch
  postfix/postfix-script: warning: not owned by postfix: /var/lib/postfix/./master.lock
  postfix/postfix-script: warning: /usr/sbin/postdrop
  postfix/postfix-script: starting the Postfix mail system
  postfix/postfix-script: fatal: mail system startup failed

Cause

Incorrect permissions for Postfix files.

Resolution

1. Connect to the server via SSH.

2. Set the correct permissions to the affected files:

   # chown postfix:postfix /var/lib/postfix/*
   # chmod 600 /var/lib/postfix/*
   # chown root:postdrop /usr/sbin/postdrop
   # chmod 2755 /usr/sbin/postdrop

3. Run the following command to fix all remaining permissions:

   # postfix set-permissions

4. Restart the Postfix:

   # /usr/sbin/postfix stop
   postfix/postfix-script: stopping the Postfix mail system

   # /usr/sbin/postfix start
   postfix/postfix-script: starting the Postfix mail system

5. Restore mail configuration by running the mchk utility:

   # plesk sbin mchk