Autodiscover service and how to disable it on-premises
For this installment of “Justin’s Tech Tip of the Week”, we will be discussing the Autodiscover 
service and how to disable it on-premises. This is extremely useful when you are in the midst of a migration or performing a staged migration (some users in O365 while others are still on-premises) so that it doesn’t interfere with your migrated Office 365 users and the ability of their MS Outlook clients from seamlessly connecting to and working with Office 365.
Standard, staged migrations to Office 365 from Exchange 2007, 2010, or 2013.This solution applies to:
- If you have already removed DNS entries on-premises for Autodiscover.
Does not apply to:
- Any kind of migration from Exchange 2003 or lower.
- Exchange Hybrid/Rich-Coexistence migrations (most cases)*
A common nuisance for customers as they are migrating to Office 365 is the incessant Autodiscover pop-ups that users tend to get with regard to the on-premises Exchange 2007/2010 environment. This situation may still persist even after all users have been moved to Office 365 from the on-premises environment.
The solution to this problem is to set the ClientAccessServer value for the on-premises Exchange bridgehead server to $Null. This is done via PowerShell on the on-premises Exchange server in question. PowerShell for Exchange 2007 and 2010 is also known as the Exchange Management Shell (EMS).
Here are the steps:
- Log into one of your on-premises Exchange 2007 or 2010 servers
- Open EMS (Exchange Management Shell)
- Run the following cmdlet – Get-ClientAccessServer This will query the environment and return the value of the actual, main CAS (Client Access Server) server for the environment.
- From the results in step 3, run: Set-ClientAccessServer –Identity “CASxx” –AutoDiscoverServiceInternalUri $NULL – where “CASxx” is the name of the CAS server that discovered value.