@freemo My friend who has his own email service setup says most of what would be useful is to look / search for this:
spf dkim dmarc
which gave me these results I'll shortlist:
SPF, DKIM, DMARC: Email Authentication Explained - The Hunter Blog
https://hunter.io/blog/spf-dkim-dmarc/
DKIM, DMARC, and SPF: Setting Up Email Security - How-To Geek
https://www.howtogeek.com/devops/dkim-dmarc-and-spf-setting-up-email-security/
SPF, DKIM & DMARC Explained: How To Set Them Up And Combat Fake Emails
@freeschool
I am familiar with those tools and have run ky own email servers before. Sadly even then i havent come close to approaching google on my ability to reduce spam
@freeschool @freemo rspamd does a pretty good job filtering spam. funnily most spams are removed by graylisting, not even by sophisticated stuff.
@bonifartius @freemo
agreed... yes more-trusted whitelisting / graylisting even exclusive access etc at least between a few
sounds like a good start (in keeping communication integrity)