I ran my own mail server from about 2008 to 2023 on a $5 per month (not including backups) VPS. Started with sendmail, some anti-spam tools, and qpopper, migrated over the years to postfix and dovecot, added some more anti-spam tools, dealt with all the SPF, DKIM, DMARC fooforaw as that became necessary, etc.

All in all, it worked fine. Might still be doing it except that I decided to run it on CentOS 6, and when it became necessary to migrate it all to CentOS 7, that seemed like it was going to be a lot of work, since there was no very good way to do an in-place upgrade.

Had I chosen FreeBSD to start with, I might well still be running it, since major-version upgrades are so straightforward. I chose linux at the time partly because I wanted to learn more about it.

In the end, I migrated to Fastmail and have never once thought, gee I wish I was still running my own mail server.

Also worth noting that with my two-year plan, Fastmail is cheaper. Not a lot, but I think it's worth pointing out that running your own mail server will probably not save you any money in the long run, so that's not a good reason to do it.

A book "Run your own email server" by Michael Lucas looks like it would inform you.

I ran one for years, Sendmail at first, switched to Postfix, but I was eventually overwhelmed by spam in 2018.

scaleway.ch has $5/month servers hosted in Switzerland and you can install POP3/SMTP

Just rent a server with a good company (such as Hetzner) that’s likely to have clean IPs, install Linux and Postfix, and Dovecot if you want IMAP access, read and carefully follow the Postfix documentation, read any of many online guides for setting up DKIM, etc., and you’re good. Once up, it’s largely hands-off. Mine has been running smoothly for over a decade. Don’t believe the FUD.