Outlook is not working

Test both outbound and inbound mail directly in Outlook on the web; if both fail there, the Microsoft 365 administrator should verify that your Exchange Online license and mailbox are active before troubleshooting any desktop application.

1. Test the mailbox in Outlook on the web

Because the issue is tagged Outlook on the web for business, perform these tests there:

1. Sign in to Outlook on the web with your work account.
2. Send a short message to an external address you can access.
3. Reply from that external address to your work mailbox.
4. Record any error or non-delivery report, including its complete error code.

Interpret the result as follows:

• Both tests work: The mailbox and basic mail flow are operating; if a desktop or mobile Outlook client still fails, troubleshoot that client separately.
• Sending works but the reply never arrives: Check Junk Email, Other, forwarding, and Inbox rules. Also select Filter → Sort → Date to ensure messages are displayed chronologically.^1^
• Sending or receiving fails in the web client: Continue with the administrator checks below. This indicates that desktop-profile repair alone is unlikely to resolve it.

2. Have the Microsoft 365 administrator check the mailbox

A standard user cannot perform these checks. Ask your organization’s Microsoft 365 administrator to:

1. Open Microsoft 365 admin center → Users → Active users.
2. Select the affected account.
3. Open Licenses and apps.
4. Confirm that a license containing Exchange Online is assigned and enabled.
5. If the Exchange Online license is missing, assign it.
6. If it is assigned but the mailbox was not provisioned correctly, the accepted resolution for a matching business-account case suggests removing and then reassigning the license to restart mailbox provisioning.^2^

Removing a license can temporarily affect mailbox access, so the administrator should verify the account and license selection before changing it and allow time for provisioning afterward.

3. Check for a Microsoft 365 service incident

If multiple people are affected, the administrator should go to:

Microsoft 365 admin center → Service health → View the service health → Exchange Online

If Exchange Online is degraded, monitor the incident there; Microsoft states that a separate support request is normally unnecessary while engineers are already restoring the service.^3^

4. Run delivery diagnostics and message trace

If the license is active and no incident appears, the administrator can:

1. Run Diag: Troubleshoot Email Delivery in the Microsoft 365 admin center.
2. Open Exchange admin center → Mail flow → Message trace.
3. Enter the affected mailbox as the sender or recipient, select the relevant date range, and run the search.
4. Open a matching message and review Details and How to fix it.

These diagnostics require a Microsoft 365 administrator account. The email-delivery diagnostic is unavailable for Microsoft 365 Government, Microsoft 365 operated by 21Vianet, and Microsoft 365 Germany.^3^

If these checks do not identify the issue, open a support request through the Microsoft 365 admin center. Include the exact error, affected mailbox, test times, external sender/recipient addresses, and message-trace results.

References

1. Can't send or receive email in Outlook.com | Microsoft Support
2. I am not able to send or receive emails - Microsoft Q&A
3. Find and fix email delivery issues as a Microsoft 365 for business admin