But still I think it would be a great idea to have a community playbook for critical things like mailservers where it is so easy to make a mistake and the fight against spammers is so hard to fight when you are only a small group of people or alone.
"Production-ready mailserver" is horribly broad (for starters, outgoing mail or incoming mail?), but Ansible Galaxy has lots of mail-related roles. For example, Zabbix: https://galaxy.ansible.com/list#/roles/1879