Step by Step paper - for hosting/splitting multiple companies on one exchange server?

Good day!

I've been on a quest for information on this topic, for quite some time now.

I am hoping by tossing this out there, someone may have run across some documentation, a process, or even just a "list of correct things to do" in order to follow MS best practices in this case.

Storyline....

I host an internal 2016 exchange server, and it's current and up to date. (v15.1 build 2507.6)

It's great, supports our small business, etc.

In support of several local charities, who need "real email" but cannot afford the $16 a month per mailbox that is the going rate, I provide mailboxes on their own domain name, at no charge to them.

Recently, I have come to realize that I really need to peel these guys away internally, so they aren't looking at my GAL and vice versa, etc etc.

Make them function and look more standalone.

Each does have their own dns & domain name.

But, I can't find anywhere, any sort of process to do this, other than high level "you need a new GAL for each" and some other stuff.

I'm an old MCSE/MCT who back in the day also carried valid Exchange credentials, so I know my way around, but get a little hesitant when it comes to breaking things that are working right now... 😉

Or guessing at long commands in the exchange management.

Has anyone run across any whitepapers or best practice documents on this topic?

Thanks!

Andrew