Yeah, people can still run their own mail servers without too much work. I've had one for a couple years but I ran into issues with Google tagging my mail as spam at first. It was a while back but I think they want domain owners to verify their ownership with Google's webmaster tools.[1]

My server worked better after adding a TXT record with google-site-verification + all the normal DKIM stuff.

EDIT: here's a better link https://support.google.com/a/answer/183895?hl=en

[1] https://support.google.com/webmasters/answer/35179?hl=en