Don't run your own mail server. You'll be attacked and get blacklisted and won't even know that it happened or why until you find out none of your emails to anyone get through.
Securing a mail server is full time plus job. Proton is great and free with their domain and cheap with yours.
This isn't true. Almost all MTA have quite sane defaults these days. Yes it's not a simple walk in the park. I mean if you have 5000 users behind you then yes, what you say can be true, one compromised user can flood you etc.
But as a "I have a small domain I host my own emails" I don't agree with your comment.
Not true. I’ve run my own server for over a decade, which has presented far fewer problems than gmail. The ability to: easily create redirects & distribution lists, back up all of my inboxes in seconds with a single rsync command, pre-filter messages with external programs, & actually see the SMTP logs and packets in real-time are game changers.
No, it's not. I say that because I am the sysadmin for two mail servers (postfix/dovecot) with hundreds of users that have been chugging along for 30 years or so with no significant security incidents -- and since I know what my full-time job entails, I can tell you that on a day-to-day basis mail requires an absolute minimum of maintenance.
This is not very hard to fix. Automatically downloading and applying public IP reputation blocklists cuts down on this by like 95%. The rest you can catch pretty trivially either with server-side filtering or just filter in the client. I do bad-IP filtering, but not spamassassin/rspamd. The client-side filtering in Mail.app kills nearly 100% of the few spam messages that get through.
Securing a mail server is full time plus job. Proton is great and free with their domain and cheap with yours.