I have looked around but all the tutorials say to use a service like Mailgun, but I would rather not.
Anyone know how I would host my own mailserver to use with Discourse.
AI-generated summary
The discussion is about hosting a personal mailserver for use with Discourse. Benjamin_Johnston wants to avoid using services like Mailgun, but others are warning about the difficulties of self-hosting a mailserver. fhe shared a tutorial on setting up an ISP-level mail server, but pfaffman advised against it, citing the complexity and potential issues with spam classification, unless sending a very large volume of emails. pfaffman also suggested Mail in a Box as an “easy” alternative, but Benjamin_Johnston noted it only supports outdated Ubuntu 14.04. justin and pfaffman echoed the advice to avoid self-hosting due to the unnecessary work involved. itsbhanusharma added that mass emailing is not recommended with solutions like mailinabox and mailcow, as they are meant for communication suites rather than mass mail sending.
This site has a good tutorial on setting up your own ISP-level mail server:
https://workaround.org/ispmail
All I’d say is that it’s not trivial, but the tutorial and the introduction should give you an idea on what’s necessary.
I ran mail servers for close to two decades. When I started, I started by porting Sendmail, UUCP, and listproc to Linux. For almost two years I’ve been considering running my own mail server again; I even have access to a Discourse forum that generates lots of mail (that I’m paying Mailgun to deliver) that I could use to warm up an IP, and it wouldn’t be the end of the world if some of that mail got classified as spam while things were getting started. I have a server that’s on an IP block that is not likely to be on lots of blacklist.
Those a near-perfect conditions for setting up a mail server. I haven’t done it.
If you’re sending fewer than 10K messages per month and have access to a credit card there is almost no reason to run your own mail server.
Another “easy” way to do it appears to be Mail in a Box. You can get help on getting it working from https://discourse.mailinabox.email/
I’ve looked into mailinabox but it only supports Ubuntu 14.04
Indeed, that doesn’t bode well for the project. Perhaps running a mail server isn’t as easy as they thought. 
As a former IT guy, I echo @pfaffman’s advice. There’s a lot of unnecessary and troublesome work ahead if you choose to roll your own mail server.
Mass emailing is not recommended through mailinabox and mailcow (and even docker-mailserver)
The reason is that all of them are built as a communication suite not as a mass mail sender.
While the easiest will be to set up an MTA and just use it to send emails I haven’t had much success in getting things like EXIM to work nicely with discourse.