We already have that, the first problem is we have like a dozen of them, a few are even well supported. The second problem is that usually the technical knowledge required to set up the systems are still lower than the technical knowledge required to keep it running.
It sounds like you’re getting into the keeping it running phase.
First, going back to your previous comment, self-hosting email is difficult. It’s not hard for a small provider to end up blacklisted and you’re probably kind of just done at that point and it will feel very unfair. I get that it’s a fun set of technical challenges, but you couldn’t pay me enough to help someone self-host email.
Second, guessing, but it sounds like you may be trying to expose your services directly and doing a lot to make that work which goes against what most would recommend for hosting your own services. Big companies don’t expose their intranet like that, follow their example. Almost every guide or system is going to warn against that. If you’re going to host more than one thing, highly recommend focusing on minimizing entry points and looking into a VPN-like solution for accessing most if not all of your services. Still spend time on securing your intranet, but most of your risk is going to come from how hard it is for people to get past the front door (or doors).