Assume that you run the Set-RpcClientAccess cmdlet to set the EncryptionRequired parameter to False. However, when you install a new cumulative update or a service pack for server update that is earlier than Cumulative Update 9, the setting of the encryption requirement switches back to True, and that may cause an outage on Microsoft Outlook in a Microsoft Exchange Server 2013 environment.
This issue occurs because of a by design logic in the Exchange Server 2013 environment.
To work around this issue, run the following cmdlet to manually set the EncryptionRequired parameter to False after the server upgrade:
Set-RpcClientAccess - Server $RoleFqdnOrName -EncryptionRequired $False
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.