Clear AutoDiscover Cache

When you change AutoDiscover settings for users, it can take up to 2 hours until the cached data is invalidated and the new AutoD configuration is sent as a response to the new AutoD request.

You have to force a restart of an Exchange service and an Exchange IIS application pool to activate your configuration changes immediately:

Service: MSExchangeServiceHost
Application Pool: MSExchangeAutodiscoverAppPool

These restarts need to be performed on each modern Exchange Server (2013/2016/2019) in your infrastructure serving AutoDiscover requests.

Use the following two PowerShell cmdlets to simplify this task:

Get-ExchangeServer | ? { $_.AdminDisplayVersion -like '*15.*'} | 
% { Invoke-Command -ComputerName $_.Name  
-ScriptBlock {Restart-WebAppPool MSExchangeAutodiscoverAppPool } }

Get-ExchangeServer | ? { $_.AdminDisplayVersion -like '*15.*'} | 
 % { Invoke-Command -ComputerName $_.Name `
-ScriptBlock {Restart-Service MSExchangeServiceHost } }

Enjoy