Hybrid Migration to 365 - What all will be affected when autodiscover is removed/pointed to 365?

Question

I have completed migrating user mailboxes to 365. The only mailboxes that remain on-premise are system/service mailboxes that don't use mail clients (and as such don't need Autodiscover) that won't or can't be migrated to 365.

So my question is this: When I remove/change the Autodiscover information, what will happen to clients (both internal/external Outlook clients as well as mobile clients)? For example when mailboxes were migrated users had to remove/re-add their mail account on their mobile devices. Will that need to be done again when autodiscover is removed? I really don't want to go through that again for almost 1000 users.

Also, what are the best steps for doing this? I understand I should set the AutoDiscoverServiceInternalUri to $null on the Exchange server (which I'll be keeping and in hybrid mode), and publish Microsoft's autodiscover information in my DNS, but is there anything else I need to be aware of?

Answer 1

Hi @Joe Grover ,

When I remove/change the Autodiscover information, what will happen to clients (both internal/external Outlook clients as well as mobile clients)?

As far as I know, normally the users' profiles will automatically pick up the changes of autodiscover settings, so it's likely that they won't be impacted at all. Below is a relevant discussion I found for reference:
Exchange Hybrid - Changing MX, Autodiscover and SPF to 365
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
"Outlook validates profile on a regular basis and updates the settings as needed. If you repoint autodiscover to Office365, even in the middle of the day, your users should not feel a thing, their profile is already should be updated with Office365 settings."

But during my research, I did notice that in a few cases, the clients might have issue get updated automatically and may have to end up recreating the profiles.

Also, what are the best steps for doing this?

Basically, the process is as straight-forward as you mentioned. You would need to update both the internal and external DNS, pointing the MX and Autodiscover DNS records to Exchange Online instead of to on-premises, then remove the SCP values on your Exchange servers by setting the AutoDiscoverServiceInternalUri to $null.

Noticed that you indicated you'll be keeping the Exchange server and in hybrid mode, so you can also check "Scenario two" in the document below which applies to any customer that is planning on keeping directory synchronization:

How and when to decommission your on-premises Exchange servers in a hybrid deployment

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