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How to Fix Shared Outlook Mailbox Cannot Receive External Emails
Question details
A shared Outlook mailbox is unable to receive incoming emails from external senders, even though it successfully sends outbound emails and other shared mailboxes in the tenant function normally.
- Product
- Microsoft Outlook
- Device & OS
- not provided
- Scenario
- Attempting to receive correspondence from external domains into a specific shared mailbox.
- Observed behavior
- Emails sent from external domains fail to arrive in the shared mailbox inbox, while internal emails and outbound messaging continue to work without issues.
Verify with the external sender if they received a Non-Delivery Report (bounce-back email), and ensure you have Microsoft 365 Administrator privileges to access the Exchange admin center.
Review Exchange Delivery Restrictions and Run a Message Trace
Check if the mailbox is restricted from receiving external emails and trace incoming messages to find the exact point of failure.
Since other shared mailboxes are functioning properly, the issue may be isolated to specific delivery restrictions or a routing failure for this particular address.
Log in to the Exchange admin center. Navigate to Recipients, select Mailboxes, and click on the affected shared mailbox. Under the mailbox settings, check 'Message delivery restrictions' to ensure 'Require that all senders are authenticated' is unchecked, as this setting blocks external senders.
In the Exchange admin center, go to Mail flow and click on Message trace. Enter the external sender's email address and the shared mailbox address, select the appropriate time range, and click 'Search' to view the delivery status and error codes.
Ask the external sender to provide a copy of the bounce-back email (NDR). Review the diagnostic information and error codes within the NDR to identify if the issue is related to spam filtering, recipient status, or routing loops.
Escalate to Microsoft 365 Support
If delivery restrictions are correct and the message trace indicates a back-end issue, you will need Microsoft Support to investigate the tenant-side configuration.
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Frequently Asked Questions
Why can my shared mailbox send emails but not receive them from outside the organization?
This commonly occurs when the mailbox is configured to require sender authentication (which blocks external domains), or due to specific mail flow rules and spam filters in the Exchange admin center that are misconfigured for that single mailbox.
How do I find out why an external email wasn't delivered?
The most accurate way is to have a Microsoft 365 Administrator run a 'Message Trace' in the Exchange admin center, or to ask the external sender to provide the Non-Delivery Report (bounce-back email) they received.
Can I fix this issue without Microsoft 365 Administrator rights?
No. Adjusting mail flow settings, modifying recipient delivery restrictions, and running diagnostic message traces require admin-level access to the Microsoft 365 Exchange admin center.
