Mailman fails to start with "Site list is missing" error

Symptoms

You try to start the mailman service, which fails with a "Site list is missing" error:

Service Error
(XID hwshb5) The “mailman” service failed to start.

Startup Log
Jan 05 10:35:34 server.domain.com systemd[1]: Starting mailman services...
Jan 05 10:35:35 server.domain.com restartsrv_mailman[16190]: Site list is missing: mailman
Jan 05 10:35:35 server.domain.com systemd[1]: mailman.service: control process exited, code=exited status=1
Jan 05 10:35:35 server.domain.com systemd[1]: Failed to start mailman services.

Description

This issue occurs when the base mailman list is missing from the server.

Workaround

1. Recreate the missing mailman mailing list:

   [root@server]# /usr/local/cpanel/3rdparty/mailman/bin/newlist
   Enter the name of the list: mailman
   Enter the email of the person running the list: email@domain.com
   Initial mailman password:

2. Restart mailman:

   /scripts/restartsrv_mailman