Minimal On-Prem Exchange Installation After O365 Migration

Question

I have completed the migration of all accounts from an on-prem Exchange 2016 installation to O365 (M365). I used the express hybrid migration route. The current on-prem Exchange 2016 however is also on the same server as the domain controller. There are also other issues with this system. It's also a Hyper-V guest that is insanely oversized for what is needed. Now that the migration is completed, I'd like to spin up a standalone minimal Exchange 2016 server just to support the hybrid connectivity. I know it doesn't need everything that a normal Exchange server would need, but are there are any steps in installing an Exchange 2016 server just to support O365 hybrid? I'm also assuming installing using /Mode:RecoverServer would be the best approach for this replacement server along with installing the Hybrid Migration Tool again?

Answer 1

HI there. There is no minimal installation of Exchange 2016, all the roles are combined into the mailbox role essentially.

https://learn.microsoft.com/en-us/exchange/server-roles#exchange-2016-hybrid-deployment

You would need to bring up a new server as you mentioned and move all and any mailboxes to the new server including the system mailboxes:

 Get-Mailbox  -Arbitration | New-MoveRequest -TargetDatabase <NewDB>  

Dont forget the audit mailbox:

https://learn.microsoft.com/en-us/exchange/troubleshoot/administration/error-remove-a-mailbox-database

After that, ensure the new server has connectivity to Exchange Online through the firewall (ports 443 and 25) ( Matching what you have now)
then re-run the Hybrid Wizard using the new server as the endpoint.

/Mode:RecoverServer does not apply here since you are building a new server.

Once the new server is up and running and working, then remove Exchange from the current server from the Add/remove Programs dialog menu...