This article explains how to diagnose and resolve issues when SmartConnect fails to send an email using a Microsoft Graph connection and displays mailbox‑related errors such as:
- MailboxNotEnabledForRESTAPI
- The mailbox is either inactive, soft-deleted, or otherwise not available
- Authentication succeeds, but the test email or integration email fails
These SmartConnect email errors typically indicate a problem with the Microsoft 365 mailbox associated with the user account used for authentication.
SmartConnect Email Error Cause
The issue is usually caused by the Azure Active Directory account used to authenticate Microsoft Graph not having an active, licensed mailbox assigned.
Resolution
Follow the steps below to resolve the error.
Step 1: Verify that the Authenticating User Has a Mailbox
- Go to Microsoft 365 Admin Center → Active users
- Find the user account used in SmartConnect for Graph authentication
- Confirm the following:
- A mailbox is assigned
- The account has an Exchange Online license
- The mailbox is not soft‑deleted or inactive
If no mailbox exists, assign the appropriate Exchange license.
Once the mailbox is provisioned, wait a few minutes and retry the connection.
Additional Notes
- SmartConnect test email and integration email tasks both use the same email-sending method. If one works, both should work.
- Token expiration may require new secrets in Azure App Registration.
If you have questions about how to fix the SmartConnect email error when using Microsoft Graph, please reach out to support@eonesolutions.com.
