"Invalid EWS URL: <url>" error in Overlay settings in CalendarService.ashx (KB5064829)

Symptoms

After you configure the Exchange Web Service URL parameter in Calendar Overlay settings, the CalendarService.ashx file displays an "Invalid EWS URL: <url>" error entry. When this issue occurs, the following error entry and "583ga" or "apmev" event tags are logged in the SharePoint Unified Logging System (ULS) logs: 

Cause

By default, to help maintain security, no Exchange Web Service URLs are allowed in SharePoint Server. 

Resolution

To fix this issue, farm administrators can run the following PowerShell commands to add the blocked URL to AllowedSafeDomain: 

add-pssnapin * 
$f=get-spfarm 
$f.AllowedSafeDomain.Add("<host>") 
$f.update() 

​​​​​​​For example: 

$f.AllowedSafeDomain.Add("smtp.office365.com")