For greylisting nowadays I use Postfix's builtin postscreen[1] along with a few DNS-based whitelists and postscreen_dnsbl_whitelist_threshold=-1 to make sure gmail etc don't get delayed. No extra software required. Though it would be nice if it had builtin ability to find IP addresses to whitelist via SPF.

I recently set up a small postfix+dovecot system, and postscreen with DNS blacklists alone seems quite effective. But I do plan to add spamassassin or rspamd or spamd at some point.

1: http://www.postfix.org/POSTSCREEN_README.html