to put it in a nutshell:

* self-hosted on a rented physical server-system running debian gnu-linux (stable)

* setup via ansible-roles

* using my own DNS-setup with isc-bind

* (open)ldap-directory (qmail-schema)

* exim4-ldap with my own configuration (not the distro-standard)

* spamassassin + clamav

* courier-imap

* roundcube for web-access

* gnu mailman ver 2.x

* letsencrypt for certificates

just my 0.02€

ps.: i'm doing this since the 2nd half of the 1990ties ... so i really know what i'm doing :))