Exchange Online error: “The proxy address is already being used by another recipient” during mailbox creation

Question

When creating or modifying mailboxes in Exchange Online, I receive the error “The proxy address is already being used by another recipient”, even though the email address does not appear to be assigned to any active mailbox.

The address is not returned by standard Get-Mailbox queries, and the issue persists after directory sync and waiting for propagation.

Answer 1

Hi Deborthia Azbill

Thank you for reaching out to Microsoft Q&A forum

Based on my research, the error “The proxy address is already being used by another recipient” typically indicates that the email address you're trying to assign is already associated with another mail-enabled object. This conflict can occur even if the address is not returned by standard Get-Mailbox queries.

Given this, to resolve this problem, you can follow these steps below:

After connecting to Exchange Online module, run the following command to search all recipient types for the conflicting address:

Get-EXORecipient -ResultSize Unlimited | Where-Object { $_.EmailAddresses -match "SMTP:<conflicting address>" } | Format-List Name, RecipientType, EmailAddresses

If the address is found, remove or change it on the conflicting object using the appropriate cmdlet:

For mailboxes:

Set-Mailbox -Identity "<Name>" -EmailAddresses @{Remove="smtp:<conflicting address>"}

For mail users or contacts:

Set-MailUser -Identity "<Name>" -EmailAddresses @{Remove="smtp:<conflicting address>"}

For distribution groups:

Set-DistributionGroup -Identity "<GroupName>" -EmailAddresses @{Remove="smtp:<conflicting address>"}

For public folders:

Set-MailPublicFolder -Identity "<FolderName>" -EmailAddresses @{Remove="smtp:<conflicting address>"}

Finally, after the conflict is resolved, retry assigning the proxy address to the intended mailbox.

For more information:

https://learn.microsoft.com/en-us/troubleshoot/exchange/email-alias/proxy-address-being-used

https://www.exchangemvp.org/fix-non-unique-proxy-address-in-exchange-online/

Note: Microsoft is providing this information as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.

You can try the above approach, if the problem still persists, kindly let me know in the comments for further support

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