I don’t think it’s as bad as it used to be. In the early 2000s I managed an email server (which was also running GNU mailman to provide mailing lists) and spam was a real problem. In 2015, I started self-hosting (Postfix, Dovecot) using my personal domain name and I was surprised at how little spam I was getting. All I had to do to stop the spam was to enable grey-listing: https://en.wikipedia.org/wiki/Greylisting_(email)