Symptoms – staff unable to login to Outlook for Desktop 

Error found in event log on patched Domain controller

The Netlogon service denied a vulnerable Netlogon secure channel connection from a machine account.  

Workaround

Deploy GPO to allow insecure connections (this should be done only until machines are patched)

Refer to https://support.microsoft.com/en-au/help/4557222/how-to-manage-the-changes-in-netlogon-secure-channel-connections-assoc