How to Fix Exchange Transport Rule Error Ex8155FB: Multiple Recipients Found
Question details
The user needs to resolve a ManagementObjectAmbiguousException error that occurs in the Exchange Admin Center when updating or creating transport rules.
- Product
- Microsoft Exchange
- Device & OS
- not provided
- Scenario
- Editing or creating a transport rule in the Exchange Admin Center using an email address that matches multiple recipient objects.
- Observed behavior
- The system throws a ManagementObjectAmbiguousException (Error Ex8155FB), stating 'Multiple Recipients Found' and preventing the rule from saving.
Ensure you have Global Administrator or Exchange Administrator privileges in your Microsoft 365 tenant before attempting to modify organizational transport rules or accessing service health logs.
Use Alternative Browsers or Administrator Accounts
Sometimes, browser caching or specific admin session states trigger false admin center errors.
Before digging into backend duplicate objects, rule out browser-level issues or temporary session glitches by using a different environment to apply the transport rule.
Open a new Incognito or Private Browsing window, log into the Exchange Admin Center, and attempt to edit or save the transport rule again.
If the error persists, open a completely different web browser (e.g., switch from Microsoft Edge to Google Chrome or Firefox) and try to apply the rule.
If multiple users have Global Administrator privileges in your organization, ask another administrator to log into the portal and update the transport rule from their account.
Contact Microsoft 365 Technical Support
If alternative browsers fail, the issue may require Microsoft to investigate backend service logs and duplicate recipient objects.
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Frequently Asked Questions
What causes the ManagementObjectAmbiguousException in Exchange?
This exception occurs when the Exchange Admin Center detects multiple recipient objects (such as a shared mailbox, user account, and a contact) associated with the exact same email address used in your transport rule condition.
How can I manually find duplicate recipient objects in Microsoft 365?
Administrators can connect to Exchange Online PowerShell and run the `Get-Recipient` cmdlet targeting the specific email address. This command will list all objects utilizing that address, allowing you to modify or remove the duplicates.
Can I fix this transport rule error if I am not a Global Administrator?
No. Modifying organizational transport rules and investigating tenant-level duplicate objects requires Exchange Administrator or Global Administrator privileges.
Why should I contact my reseller instead of Microsoft directly for this error?
If your Microsoft 365 subscription was purchased through a Cloud Solution Provider (CSP) or authorized reseller, they are designated to manage your tenant's tier-1 support and must be the ones to escalate backend server issues to Microsoft.
