I used to in the late 90s early 2000s, but it became impractical. I also maintained one as part of my job in the 2000s, and it became obvious that the amount of upkeep/time was not worth it just to host it yourself.
The main headache? Anti-spam. A lot of IP ranges are just outright broadly blacklisted (e.g. residential IPs, some hosting services), but also a lot of individual IPs reused by hosting providers got blacklisted for actually sending spam. Then you have trust scores which are a huge chicken/egg headache (how do you gain trust while being span-binned from the get-go?). You'll spend your days asking to get unblocked from various random third party providers that you may never have heard of (e.g. email a small business about their online shop, and their email vendor bounced you because they never heard of you, they take ten days to respond, and now it takes two weeks to email some random small business).
Plus the ever-changing requirements (and they ARE requirements, if you lack reverse DNS/DMARC/SPF/DKIM/TLSA/valid certificates you will be blocked).
It is just a headache, time, and it actually costs more for the pleasure. Free Google Workspaces killed 90% of people self-hosting, too bad it costs tons of money these days.