Running your own mail server can be fun, and it is important for an open Internet. But it can also be quite challenging: securing your server, filtering out spam, and having your mail accepted by others is complicated. To get better at it and help others, I'm getting "Run Your Own Mailserver" https://www.kickstarter.com/projects/mwlucas/run-your-own-mail-server/ from @mwl, an accomplished writer.
@stb running a Mailserver is a big opportunity for learning!
Did it professionally, then setup my own stack, now using MailCow and it does an amazing job.
Currently in progress of moving all my accounts away from Gmail, which is very tedious.
If anything, people should always use their own domain! Or you will susceptible to #enshitification and a hard road to get away from. @pluralistic makes this point very well.