Event ID 15021 HTTPEvent error occurred while using SSL configuration for endpoint 0.0.0.0:444
Applies to Exchange Server 2013
This error is traced from the Windows Event Viewer – Windows Logs – System
If your Exchange Server is setup on a Single Server; the Exchange Administration Center (EAC) returns blank page
If there are multiple servers involved; the issues will be restricted to the below
- The OWA will allow login, but returns blank similar
- Outlook as well any other Exchange Clients will fail to connect
- Exchange Management Shell will fail to connect. (Returns Error : FullyQualifiedErrorId : -2144108477,PSSessionOpenFailed
This error crops up due to the usage of non-existing or unassigned certificate.
Open IIS Manager from the server faced with the issue

From Sites; select Exchange Back End; right click and select Edit Bindings
Edit the Site Binding for https – 0.0.0.0:444

If the SSL Certificate field shows Not Selected or any wrong Certificate; please ensure the correct certificate is selected.
Click Ok to Save once done