I can host my own Mastodon server, or all kinds of other novelty / fun things which don't seem easily decentralized.
Email feels like one of the most decentralized internet concepts, and ironically it's seemingly the one thing I can't self-host unless, from what I've heard, I enjoy being permanently marked as spam / blacklisted. What's going on? How do we fix this?
I host my own email server with Vultr on an OpenBSD VM using OpenSMTPD and Dovecot, relaying all outbound mail through SMTP2Go (their free tier more than meets my needs). I have all of the necessary DNS entries set to mark my mail as legit, and I sign all outgoing mail using strong 2048-bit RSA keys. Thus far, I'm able to send mail and not have it marked as spam (at least to everyone that I've corresponded with thus far). It was a lot of work to get to that point, but not terrible.