Google has started automatically blocking emails sent by bulk senders who don’t meet stricter spam thresholds and authenticate their messages as required by new guidelines to strengthen defenses against spam and phishing attacks.
As announced in October, the company now requires those who want to dispatch over 5,000 messages daily to Gmail accounts to set up SPF/DKIM and DMARC email authentication for their domains.
I know a there are a lot of issues with self-hosting email, but I just don’t thing this is one of them. First, it probably won’t affect a self-hosted servers anyway unless you send a lot of emails, this requirement is only for servers sending 5,000 messages daily to Gmail. And even if you are, the requirements are not that harsh, it’s a couple DNS records and a DKIM signing daemon, and if you are using a pre-build email package like mailcow it’s probably already doing it.