You can verify independently if a mailbox is accessible using EWS with the following steps:
- Go to Microsoft Remote Connectivity Analyzer.
- If using Microsoft 365, click the Exchange Online tab from the menu on the left side.
- Select Service Account Access (Developers) then click Next.
- Specify the following information:
- The Target mailbox email address.
- The Authentication type. This must be Moder authentication (OAuth).
- The Modern Authentication (OAuth) credentials by signing in and using the service account credentials. If using admin credentials on the connector, enter the same username and password.
- Select the Specify Exchange Web Services URL option from the Autodiscover selection.
- Enter the FQDN of the Exchange Web Service (EWS) Server. For example, if the EWS URL is https://mail.contoso.com/EWS/Exchange.asmx, then enter mail.contoso.com.
- Select the Folder type you will use.
- If using an on-premise Exchange Server, do not check "Use Exchange Impersonation." If you are using Microsoft 365, and using impersonation, do check the box.
- Check Ignore Trust for SSL.
- Click Perform Test.
- Once results are displayed, check the overall result, and click Expand All.
It may be necessary to first manage permissions.