Exchange 2010 The proxy address 'MBX:0' is already being used by...

While preforming a cleanup/bulk conversion of mailboxes that were migrated incorrectly from Exchange 2003 (User Mailboxes came over as Shared Mailboxes and vice versa) the EMS threw an error about an "MBX:0 proxy address already in use". The mailbox moves sometimes stamps the mailbox with a MBX:0 or MBX:1 proxy address; you'll need to remove those before you can convert the mailbox type.

Here's the error:

There are a few ways to remove these, depending on how many users have the proxy stamp.

Using Exchange Management Console (EMC)

In the EMC under Recipient Configuration, right-click Mailbox, then Find.

In the search field, type MBX and it'll list users with the MBX:0/1 proxy

Open properties of the mailbox, go to Email Addresses, select the MBX and hit the X

Using ADSIEdit

In ADSIEdit, run a query with the following:

Root of Search: yourdomain.com
Query String: (proxyAddresses=smtp:MBX:0)
Query Scope: Subtree search

Remove the MBX address from the Attribute "ProxyAddress"

Using the Exchange Management Shell (EMS)

This is the most useful if you have a ton of users with the wrong address

Fire up the EMS and run:

$Users=Get-User

 

foreach ($user in $Users)

 

{

$adsiUser = [ADSI]"LDAP://$($User.OriginatingServer)/$($User.DistinguishedName)";

 

$adsiUser.proxyaddresses.remove("MBX:0");

 

$adsiUser.SetInfo()

 

}

Now you can convert to pesky mailboxes