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?
Email is the hardest thing to self-host, but it’s definitely doable. You’ll need a static IP, and you’ll need to talk to your ISP to make sure outbound connections on port 25 are open.
Set up your servers and your DNS settings (another commenter gave a good guide), then use this tool to check that DKIM and SPF are working and that you’re not seen as spam with SpamAssassin:
https://dkimvalidator.com/
Once that’s done, take your static IP and check it with this tool:
https://mxtoolbox.com/blacklists.aspx
If it’s on any of the lists, you’ll need to go to those lists’ sites and try to get it removed. You might need to make an email address for “postmaster@yourdomain” at this point.
Beyond that, you may need to “warm up” your IP address, by sending email to yourself on various services (Gmail, Yahoo, Microsoft) and marking them as not spam.
Then you should be golden.
I had to do this for both my SMTP servers for Port87. If you use more than one server, this process gets a little harder, so probably stick to one at first.
I’m pretty sure gmail’s filters are per-user. I’ve had it react after just one flag/unflag, and I doubt that it would do that it would only take one action to change it for everyone.
It’s more of a signal that the IP address does send trustworthy email. AFAIK, IP reputation isn’t handled on a per-user basis. Domain reputation probably is.