I "sort of" hosted my own email using Sendgrid API free tier to send and webhook to receive, and a custom client in a Python MPA. I was chuffed I wasn't paying 5 a month for GSuite.
I'm not sure about all the cant, it's definitely possible and I never had an issue with deliverability. I had no idea what I was doing but I made sure I got all the right dkim secret and signing keys or whatever that was required set up "extra special like" for both solutions.
I was not sending mail merges though so maybe that would have thrown things off I don't know.
I looked later at, and set up, https://mailinabox.email/ and that worked fine too.
I'm not sure about all the cant, it's definitely possible and I never had an issue with deliverability. I had no idea what I was doing but I made sure I got all the right dkim secret and signing keys or whatever that was required set up "extra special like" for both solutions.
I was not sending mail merges though so maybe that would have thrown things off I don't know.