Was talking about Mastodon with an old-school sysadmin guy. We reached the realization that defederating from instances with no/bad moderation is essentially the same thing as blocking open relays back when you ran your own email server: open relays always end up getting used for spam, you block 'em to protect your users.
Email was and still is the first federated social network, so it already faced a lot of the same problems; we should study its solutions (and its failures).
Many people and companies still do. And gmail's unwillingness to play nicely with them because of their own short-sighted dictatorial policies is a major reason for people drifting away from gmail. In fact, I hear more about people leaving gmail for that reason, than for ideological reasons (granted the ideological people are loud).
Obviously I'd suggest doing it ~in the cloud~ on a reserved IP with stable documented software, but the rest is just Normal Admin Stuff. Certainly doable and Gmail doesn't whine. (The key is DKIM+SPF+rdns and checking blacklists.)
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