Add mail server setup scripting.

[config] / buster / etc_files / mail / etc / dovecot / conf.d / 99-smtp-sasl.conf

service auth {
  unix_listener auth-userdb {
  }

  unix_listener /var/spool/postfix/private/auth {
        mode = 0660
        user = postfix
        group = postfix
  }
}