I tried maybe 15 years ago and it went about as well as you’d expect for back then. But I’m starting to get the itch again.
Have any of you tried relatively recently? How impossible is it to get reliable deliverability to gmail and whatnot these days?
If you want to be able to accept mail, you’ll need to directly expose your mail server on your public IP (router configuration required). You’ll also need to allow your server to egress your WAN as well. That being said - if you really want tighten your security, and don’t care about missing some emails, you could limit your server to seeing only those servers you know you’ll be communicating with, such as work, bank, or GMail servers only.
You can make it so that retrieving your email with your client of choice requires a VPN connection to your home network also.