I started hosting my own email in 2004 before finally giving up and migrating my email to Fastmail last year.
Besides the problems mentioned in this post the real problem I had was dealing with spam. The open source community around spam has really degraded over time, to the point where most solutions are extremely high maintenance and require regular tweaking. Methods that used to work, like greylisting, cause problems when dealing with GMail because google doesn't play nicely with it. The big spam blacklists have also gotten a bit less trustworthy over the years.
I started self hosting in 2017. (With a fresh domain. I'm the only user.) My sever closes the incoming connection if it doesn't has a rDNS or the HELO doesn't match the rDNS. Apart from that I have no anti spam measures! Friends and family have my firstname.lastname@domain address. Websites and companies get a <random>@domain address. So far I have only reserved 3 spam mails. Two times they got the address from a public mailing list I participated. One time it was from a webshop that sold or leaked my address.
I’ve noticed since switching to Fastmail from gmail my spam filtering is very problematic. I always end up with legit emails in spam, and I just can change if I want even more legit in spam or more spam in inbox, which still gets through.
I think it’s both a tough problem, as well as something that only becomes easier when you have both talent and scale to have a wide perspective.
Besides the problems mentioned in this post the real problem I had was dealing with spam. The open source community around spam has really degraded over time, to the point where most solutions are extremely high maintenance and require regular tweaking. Methods that used to work, like greylisting, cause problems when dealing with GMail because google doesn't play nicely with it. The big spam blacklists have also gotten a bit less trustworthy over the years.