Mail stuck in the queue in the server with Plesk: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (13)

Symptoms

• MariaDB upgrade has been performed recently on the server with SELinux enabled 
• Mail stuck in the queue with below messages in /var/log/maillog:

  CONFIG_TEXT: Nov 2 13:32:47 pl-01 amavis[26892]: (26892-01) (!)connect_to_sql: unable to connect to DSN 'DBI:mysql:database=emailsecurity;host=localhost;port=3306': Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (13)
  Nov 2 13:32:47 pl-01 amavis[26892]: (26892-01) (!!)TROUBLE in process_request: connect_to_sql: unable to connect to any dataset at (eval 132) line 253.
  Nov 2 13:32:47 pl-01 amavis[26892]: (26892-01) (!)Requesting process rundown after fatal error

Cause

SELinux context for the MariaDB socket file /var/lib/mysql/mysql.sock has been lost because of upgrade.

Resolution