If you want to build your own mail server (or upgrade your existing one), consider using the Homebox scripts. They are a set of Ansible scripts to deploy a fully functional and secure mail server at home or online. They are Debian based, use Postfix, Dovecot, RSpamd, OpenLDAP for authentication, etc. They allow you to build a full-fledged mail server, including webmails, calendar and addressbook synchronization, etc.
If you don’t need a full-fledged mail server, I guess that it should be easy to leave out some parts of it, given that the whole system is built with Ansible scripts and playbooks.
If you just need a simple SMTP server that only sends emails (useful for sending notifications from web applications), or a forward-only SMTP server (that forwards all the incoming emails to an external account), consider trying docker-scripts / postfix · GitLab . It is Docker based and can use OpenLDAP authentication.
Have you tried any other useful mail systems (or mailserver building tutorials) that you could recommend to the others?