Mail hosting playbook matches the provisioned servers

The internal Mail hosting playbook now records the setup as carried out: the mail server shares a DigitalOcean private network with the web server, the existing PowerDNS server is the secondary nameserver, and customer mail reaches the web server through a private listener added to its existing Postfix. Corrected commands cover SSH sign-in, the PowerDNS schema path and zone cache, the Postfix pipe transport and its user, the submission sender check, and the production database name.