You can verify independently if a mailbox is accessible using EWS with the following steps:
- Go to https://testconnectivity.microsoft.com.
- If using Office 365, click the Office 365 tab.
- Select Service Account Access (Developers) and click Next.
- Specify the target mailbox email address.
- Specify the service account user name. If using admin credentials on the connector, enter the exact same user name.
- Specify the service account password. If using admin credentials on the connector, enter the exact same password.
- Check Specify Exchange Web Services URL and specify the URL (example: https://server/EWS/Exchange.asmx).
- If using Exchange Server, do not check Use Exchange Impersonation. If you are using Office 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.