This was tough to find a concrete answer for. I don’t know why I didn’t just try it, although I was getting there. Once DNS (MX records) are all set up, and my smtp gateway was configured to forward a new domain, I was having trouble convincing exchange to use the new domain. There were plenty of examples where you add the domain to the default recipient policy in ESM. In course of doing this though, it was made clear to me by a popup that exchange wanted to give every user an email at this new domain if I checked the check box to enable it. I left the box empty, manually added an email at the new domain in ADUC, but got relay errors. I figured I could use a new recipient policy and a group with an ldap search filter to apply the new domains to those users who worked with that project, but I really only wanted one or two emails and they’d be special aliases anyways so I didn’t want to have another group kicking around.
I started to try this yesterday, but confirmation this morning when I did some more reading here that you can add recipient policies and apply no filter. This appears to have the correct effect of allowing me to use the domain, but recipient update services doesn’t try to do anything automatically on me.
It’s funny that I keep posting about exchange. I’ve been working with a lot of other cool software, but most of that makes sense as I learn it. It’s only been exchange where I’ve said “what the fuck?” and felt the frustration that leads to a post, hoping to shorten someone else’s googling.