Yes, I still run my own email server. It is not for the faint of heart, but once it's configured and your IP reputation is clean, it's mostly smooth sailing. I have not had any deliverability problems to date, initial setup/learning period notwithstanding.

If you're not scared away yet, here are some specific challenges you'll face:

• SMTP ports are typically blocked by many providers as a spam prevention measure. Hosting on a residential connection is often a complete non-starter and is becoming more difficult on business class connections as well (at least in the US, anyway).
• If you plan to host in a VPS, good luck getting a clean IPv4 address. Most are on one or more public blacklists and likely several company-specific ones (cough Microsoft cough). I spent about 2 weeks getting my new VPS's IP reputation cleaned up before I migrated from the old VPS.
• Uptime: You need to have a reliable hosting solution with minimal power/server/network downtime.
• Learning Curve: Email is not just one technology; it's several that work together. So in a very basic email server, you will have Postfix as your MTA, Dovecot as your MDA, some kind of spam detection and filtering (e.g. SpamAssassin), some kind of antivirus to scan messages/attachments (e.g. Clamd), message signing (DKIM), user administration/management, webmail, etc. You'll need to get all of these configured and operating in harmony.
• Spam prevention standards: You'll need to know how to work with DNS and create/manage all of the appropriate records on your domain (MX, SPF, DMARC, DKIM records, etc). All of these are pretty much required in 2023 in order for messages from your server to reach your recipient.
• Keeping your IP reputation clean: This is an ongoing challenge if you host for a lot of people. It can only take one or two compromised accounts to send a LOT of spam and land your IP/IP block on a blacklist.
• Keeping up with new standards: When I set my mail server up, DMARC and DKIM weren't required by most recipient servers. Around 2016, I had to bolt on OpenDKIM to my email stack otherwise my messages ended up in the recipient's spam folder. -Contingency Plan: One day you may just wake up and decide it's too much to keep managing your own email server. I'm not there yet, but I've already got a plan in place to let a bigger player take over when the time comes.