Check configuration :

Get-WebServicesVirtualDirectory |fl identity,internalurl,externalurl

Set internal EWS configuration

Set-WebServicesVirtualDirectory -Identity “MAIL01\EWS (Default Web Site)” -InternalUrl https://MAIL01.domain.local/EWS/Exchange.asmx -BasicAuthentication:$true

Set external EWS configuration

Set-WebServicesVirtualDirectory -Identity “MAIL01\EWS (Default Web Site)” -ExternalUrl https://something.domain.com/EWS/Exchange.asmx -BasicAuthentication:$true