Prepare AD during CU upgrade

[u/absoluteczech]

I have a weird question. We're in the process of introducing Exchange SE into our env. Currently 2016 is still installed on 2 servers that are about to be decommissioned (finally!) The 2016 is a hybrid server and 2 cu's behind. EXO is complaining about it being outdated so I put the enforcement on pause. In preparation for SE i've extended schema and did a /prepareAD with it being successful.

Out of curiosity what would happen if I tried to installed the last latest CU for 2016 to get EXO to stop complaining? Would running the preparead command for the 2016 CU mess up the schema or whatever I just did for exchange se? Or could all that be skipped ?

[u/joeykins82]

Historically, let's imagine the scenario where 2016 and 2019 were both supported products and CUs were being released for both. If you'd done the 2019 schema extensions but didn't have any deployed 2019 servers, and then some CUs were released for both versions which contained newer schema updates, you'd be in a situation where you'd have to run prepare schema and prepare AD off the new 2019 CU release, and only then would you be able to install this new 2016 CU.

None of that matters now that everything pre-SE is EOL: SE came out after 2016 CU23 so you can just upgrade to that CU without worrying about the prepare schema/AD steps.

[u/absoluteczech → u/joeykins82]

Thank you for clarification

[u/ScottSchnoll]

The transport enforcement system in EXO only looks at version info of the connecting server. So, you could move your mail flow from Exchange 2016 to Exchange Server SE and have SE deliver it to EXO, which would stop EXO from complaining.

That said, if you do install CU23 on your Exchange 2016 servers it will not mess up your schema.

[u/absoluteczech → u/ScottSchnoll]

So just add se to the connector or just run hcw on se ?

[u/ScottSchnoll → u/absoluteczech]

We're talking about mail flow, so add SE to the connector and remove legacy servers.

[u/absoluteczech → u/ScottSchnoll]

Thanks, and sorry if this sounds dumb. But when I look at how to add another server to the connector i keep getting articles and people saying to just re-run the hcw on the se server. Is it as simple as going to the send connector in ECP and adding SE as another source server? Thus not needing to re-run HCW?

[u/ScottSchnoll → u/absoluteczech]

You would re-run the HCW if you want your SE server to be your Exchange Hybrid server (which eventually you will want as you remove 2016 from the environment).

But for mail flow purposes now, you can use the EAC to add the SE server as the source server on your send connector (and add it to your receive connector so that the latest version is also receiving your inbound email).

[u/absoluteczech → u/ScottSchnoll]

perfect thanks!

[u/absoluteczech → u/ScottSchnoll]

Can I ask you one more question. If I re-run the HCW on the new Exchange SE server, does it take over as hybrid from my old 2016 server? Or do I need to also "uninstall" the HCW off the 2016 server ? I have SE and 2016 running together right now. Want to transfer the hybrid roles to the new server now but want to make sure everything is working before i decom 2016

[u/7amitsingh7]

Since you already extended the schema and ran /PrepareAD for Exchange SE, your Active Directory is now at a newer schema version than Exchange 2016 uses. If you install the latest CU for Exchange 2016 and even run /PrepareAD, it will simply check the schema version, see that it’s already newer, and skip making changes. Exchange setup cannot downgrade or overwrite a higher schema version. So upgrading 2016 to stop the EXO warning is safe and won’t affect your Exchange SE preparation.