Earlier quoted context omitted.
Its not the mail server, its deliverability. If you can set up a $5/month server to send email so can every spammer ever and the big mail providers know this. Mail sent like this won't be delivered anywhere with even the most basic spam filtering which includes blacklists of known spam-source IP address blocks like Digital Ocean/AWS/Heroku.
I have a personal mail server that collects my mail, but use my "default" Comcast MX to send. I'm sure metric craptons of email flow through that, but a lot of ham does too, so I've never been blacklisted. I'd suggest that rather than the goal being to instantly leave this service or that the instant that they offend you, that you envision your policy as one of being ready to leave if you ever need to. The biggest ke…
Also, I'm not sure what you're referring to as Comcast MX, but if you mean a Comcast provided server, that's a huge privacy hole. If you mean your own server on a Comcast line, then your IP is leaked to everyone you email, which is also a privacy hole since it ties your IP directly to your identity.