You didn't understand the question. I already have the mail server running. That's not the problem.

This is probably no help to you, but since you're doing this already, you may know. Is it feasible to self host your own email server but then use something like Mailgun for SMTP?

Yes. I do this. It gets rid of the spam folder problem while allowing you to host the incoming email yourself.

I might go down this route. Great advice! What service do you use? Thanks

I'm with Sparkpost for my personal stuff, at work we use Mailgun.

For what purpose?

I believe it allows you to send outgoing mail using Mailgun which is trusted (doesn't end up in recipient's spam folder) but receive incoming mail to your server.

Most if not all ISPs have MTAs for customer use. I don't know how Comcast would like me submitting from Postfix, but I don't have to worry about that and my personal ISP can handle being a next-hop MTA just fine if I need it.