Forcing a SMTP on a Mailbox fails

Posted by robd on October 24, 2018
Exchange Online

As I mentioned in another post, you can force a EoL mailbox to take on a SMTP with this command:

Set-Mailbox User.Name -WindowsEmailAddress

But occasionally it won’t work:

The proxy address "" is already being used by the proxy addresses or LegacyExchangeDN of "". Please choose another proxy address.

    + CategoryInfo          : NotSpecified: (Adri Donkers:ADObjectId) [Set-Mailbox], ProxyAddressExistsException

    + FullyQualifiedErrorId : [Server=VI1PR04MB4349,RequestId=8938a92c-006d-4f9f-b230-937f591d20e4,TimeStamp=22/10

   /2018 06:18:53] [FailureCategory=Cmdlet-ProxyAddressExistsException] 169E5E0,Microsoft.Exchange.Management.Rec 


    + PSComputerName        :

So to find who’s using the address you can search all of Azure using:

Get-Recipient | where {$_.EmailAddresses -match ""} | fL Name, RecipientType,emailaddresses


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