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How to Fix Non-Unique Proxy Address Errors in Exchange Online
Question details
The user needs to resolve a Microsoft 365 license assignment failure caused by a non-unique proxy address error in Exchange Online.
- Product
- Exchange Online
- Device & OS
- not provided
- Scenario
- Assigning a Microsoft 365 license to a user account.
- Observed behavior
- The license assignment fails due to a duplicate proxy address detected by Exchange Online, even when no conflicting accounts are visible in the admin center.
Ensure you have Global Administrator or Exchange Administrator privileges in Microsoft 365 and have the Exchange Online PowerShell module installed on your computer.
Identify and Remove the Duplicate Proxy Address using PowerShell
Use Exchange Online PowerShell to search all recipient objects for the hidden conflicting SMTP address and remove it.
Sometimes, deleted accounts, shared mailboxes, or public folders retain email addresses that conflict with new license assignments. Because these are not always visible in the standard Microsoft 365 admin center, PowerShell is the most effective way to locate them.
Open PowerShell as an administrator and execute 'Connect-ExchangeOnline' to sign in using your admin credentials.
Run the following command, replacing the placeholder with the conflicting address: Get-EXORecipient -ResultSize unlimited | Where-Object {$_.EmailAddresses -match '<partial conflicting SMTP address>'} | Format-List Name,RecipientType,EmailAddresses
Review the command output to identify whether the conflicting address belongs to a mail user, shared mailbox, public folder, or a soft-deleted object.
Navigate to the appropriate section in the Exchange Admin Center to remove or modify the duplicate proxy address from the identified object.
If the duplicate address has been removed but the license assignment still fails, have a Global Administrator open a support request with Microsoft 365.
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Frequently Asked Questions
Why doesn't the duplicate proxy address show up in the Microsoft 365 admin center?
The conflicting address might belong to a soft-deleted mailbox, a public folder, or a hidden recipient type that doesn't display in the standard active users list, requiring PowerShell to uncover.
What is a proxy address in Exchange Online?
A proxy address is an alternative email address (also known as an alias) assigned to a single recipient object. It allows a user or mailbox to receive emails sent to multiple different email addresses.
How long does it take for proxy address changes to take effect?
Changes made directly in Exchange Online typically apply within minutes. However, if you are using Azure AD Connect in a hybrid environment, you may need to wait for the next directory sync cycle, which can take up to 30 minutes.
