I host my own using a VPS with OpenBSD, OpenSMTPD, and Dovecot. I like having unlimited mailboxes and aliases.
In-bound is easy with DNS checks filtering all spam. Out-bound is somewhat out of my control, so I use a relay like smtp2go or sendgrid for reliable delivery.
Interestingly, the SS Arthur M. Anderson which was 10mi behind the Fitz when it went down, is still in use 70 years since launch and currently in Lake Huron.
Not having the ability to backup and archive my messages means Signal controls my data, not me. It reminds me of my past fights with closed source, proprietary software and file formats.
Sadly, still unusable for me since the Quantum update.
A clean install and profile, no add-ons, and google.com/maps (for example) will max out my cpu. There must be some bug related to old hardware and OS (Macbook Pro 2009 + 10.11.x) or more people would be experiencing this.