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Fix External Email Missing from Shared Mailbox in Exchange Online
Question details
Users need to locate and release emails from a specific external domain that are failing to reach an Exchange Online shared mailbox.
- Product
- Exchange Online / Microsoft Outlook
- Device & OS
- not provided
- Scenario
- Receiving emails from external senders in a shared mailbox.
- Observed behavior
- Emails from one specific external domain do not appear in the shared mailbox via Outlook or Outlook on the web, while other messages are received normally.
Ensure you have Microsoft 365 Exchange Administrator or Security Administrator credentials, as you will need access to the Exchange Admin Center and Microsoft Defender portal to trace and release messages.
Run a Message Trace in the Exchange Admin Center
Use the Message Trace tool to identify exactly where the incoming emails are being routed or blocked within your Exchange Online environment.
A message trace follows email messages as they travel through your Exchange Online organization. You can determine if a message was received, rejected, deferred, or delivered.
Log in to the Microsoft 365 admin center using your administrator credentials, and select 'Exchange' from the left-hand navigation pane.
In the Exchange Admin Center, go to 'Mail flow' in the left menu and click on 'Message trace'.
Click 'Start a trace'. Enter the affected external domain or specific email address in the 'Senders' field, and the shared mailbox address in the 'Recipients' field.
Click 'Search'. Review the message status in the results list. If the status says 'Filtered as spam' or 'Quarantined', proceed to check your security policies.
Review Quarantine and Anti-Spam Policies
If the message trace indicates the emails were blocked, you must release them from quarantine and adjust your policies to prevent future blocking.
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Frequently Asked Questions
Why are emails from only one specific external domain missing in our shared mailbox?
This usually occurs because the sender's domain triggers your organization's specific anti-spam, anti-phishing, or transport rules. The system quarantines or drops these messages for security reasons, while emails from other domains pass through unaffected.
Can end-users view and release quarantined messages for a shared mailbox?
Yes, but only if the administrator has configured quarantine policies to allow end-users to manage their quarantined messages. If enabled, users can view them in the Microsoft 365 Defender portal.
How long does a message trace take to complete in Exchange Online?
For emails sent within the last 7 days, the trace search runs almost instantly. For messages older than 7 days, it is treated as a historical search and may take a few hours to generate a downloadable report.
