I've been running my own mail server with several domains for me, my now wife, and friends since 1999. It's definitely changed with time and gotten more strict with things like spf, dkim, dmarc, and reverse dns all becoming necessary over the years.
But it's not that difficult to be honest. Currently my internet provider is init7 and they offer fixed ip4 and set the reverse dns for me which lets me run the server downstairs in the cellar instead of at a colo somewhere (which I was doing for maybe 15 years).
Every now and then I look into moving to a paid service but we have GBs of mail since 1999 and it's just too costly when it's pretty much free for me to host it myself, even taking into account the time it takes for my effort, which is practically zero.
Plus I use my server for a ton of other stuff so it will always exist so I may as well host email too.
Wanted to add something... the biggest issue I've had in the last few years is having to whitelist senders to skip the temporary rejection (smtp 4xx code) process to reduce spam.
Basically, someone new emails me and my server responds with a temporary rejection message saying to try again later and then when their server retries the message 5 minutes later it allows it to go through. This is a standard process to block spammers.
However lately when their email service resends the message it will come from a different server. Something like mailserver-1, then mailserver-2, then mailserver-3, each with a different ip address and each time it gets rejected until it reuses one of the addresses. But with apple for example they have hundreds of servers to cycle through and eventually the message times out and is rejected at their end.
So I have to whitelist senders to skip the temporary rejection. It comes up every few months for me, having to whitelist someone. I think it's a result of every small- mid-size company moving to providers and not hosting their own email, and these providers having dozens of servers. The domain of the server never matches the domain of the sender...
I have no problems with my current home ip address (here in Switzerland with the provider init7) but years ago (~20) when I moved my server to a Colo the ip address was marked as a spammer because of the previous owner of the address. It didn't take long to make the ip address clean though - some online processes and also sending some emails. This was so long ago I barely remember what I had to do and I'm sure the process is different now because back then you could contact an actual human...
But it's not that difficult to be honest. Currently my internet provider is init7 and they offer fixed ip4 and set the reverse dns for me which lets me run the server downstairs in the cellar instead of at a colo somewhere (which I was doing for maybe 15 years).
Every now and then I look into moving to a paid service but we have GBs of mail since 1999 and it's just too costly when it's pretty much free for me to host it myself, even taking into account the time it takes for my effort, which is practically zero.
Plus I use my server for a ton of other stuff so it will always exist so I may as well host email too.