

I run Postfix, Dovecot and rspamd on my server. The configuration is here: https://git.dblsaiko.net/systems/tree/configurations/polaris
There’s also the Simple NixOS Mailserver project which is an abstraction on top of these and has a few more things. I’ve never used it myself though.
Of course, you also have to set up all the standard email setup like DKIM, DMARC, SPF and so on here.
INWX has been great so far, have been with them for about 6 years at this point. Also had good experiences with their customer support.