I have one that has me stumped. A new customer has a DC and an Exchange 2016 server. Everything has been working fine until yesterday. Something happened and the server now will not let any of the Outlook clients connect. I can connect through OWA but I cannot send or receive emails. When trying to send, I get the You don't have permission to perform this action. Everything looks normal in the EAC. In the Event logs I am getting the 9041 which from reading on it points to DNS but the only DNS entry in the NIC configuration is the DC. Needless to say the customer is anxious to get email back up. Any ideas?