Fix Microsoft Defender Quarantining Internal Emails from Android Devices
Question details
Internal emails sent to or from Android devices within a Microsoft 365 environment are incorrectly flagged and quarantined as spam by Microsoft Defender.
- Product
- Microsoft 365 Defender
- Device & OS
- Android
- Scenario
- Users are attempting to send or receive internal company emails using their Android mobile devices.
- Observed behavior
- Messages involving Android devices are quarantined as spam despite standard filtering and allow-list checks, while messages involving Apple devices or external addresses remain unaffected.
Gather message traces, timestamps, affected user details, and device information to provide to the support team, ensuring no sensitive content is exposed.
Submit a Support Ticket via Microsoft 365 Admin Center
Since standard allow-lists and security policies fail to resolve the issue, an IT administrator must escalate this complex Defender and Exchange routing anomaly directly to Microsoft Support.
Because this issue involves intricate routing behaviors between Microsoft 365 Defender, Exchange Online, and specific mobile device processing, standard tenant allow/block lists or connection filters may not resolve it.
Microsoft support engineers have the necessary backend access to trace the exact cause of the false positive spam flags triggered specifically by Android device headers.
Navigate to admin.microsoft.com and log in using your Microsoft 365 IT Administrator credentials.
Click on the 'Support' section on the left-hand navigation menu, then select 'Help & support'.
Type a brief description such as 'Internal emails from Android devices quarantined by Defender' and press Enter to search.
Scroll to the bottom of the suggested articles and select the option to 'Contact Support' to open a new service request.
Fill out the ticket description with your gathered message traces, affected user accounts, Android device details, and quarantine information.
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Frequently Asked Questions
Why are only internal emails from Android devices being quarantined by Defender?
This specific behavior is often tied to how mobile device management (MDM) or Exchange ActiveSync headers are processed by Microsoft Defender's inbound policies. It may inadvertently flag Android-specific routing data as suspicious while passing Apple devices.
Can I fix this by adding the Android users to the Tenant Allow/Block list?
In standard scenarios, updating the allow list works. However, if internal messages are still flagged after modifying tenant allow/block lists, connection filters, and inbound policies, a backend anomaly exists that requires Microsoft Support intervention.
What information should I include in my Microsoft support ticket?
Include message traces, affected user email addresses, Android device models, OS versions, timestamps of the blocked emails, and quarantine headers. Ensure you redact or exclude any sensitive organizational data before submitting.
