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Create Shared Mailboxes with Same Alias at Different Domains in Office 365

17 Feb 2013 by Emma Robinson

I came across an interesting puzzle over at the Spiceworks Office 365 Forums this weekend. A user was trying to add two shared mailboxes to their Office 365 tenant with the same alias.

For example:

  • shared_mailbox@domain1.com
  • shared_mailbox@domain2.com

Trying to create a Shared Mailbox in the normal way resulted in an error.

Read more Optimizing PowerShell for large Office 365 tenants

I tried to do this in my own environment. I already had a shared mailbox called test_shared@cogmotive.onmicrosoft.com, and I wanted to add another one called test_shared@cogmotivereports.com. Here’s what happened.
PS C:\Users\burns_000\Desktop> New-Mailbox -Name "Test Shared Mailbox" -Alias test_shared -Shared -PrimarySMTPAddress test_shared@cogmotivereports.com
Windows Live ID "test_shared@cogmotive.onmicrosoft.com" already exists as a managed Windows Live ID. To use the
existing Windows Live ID, use the UseExistingLiveId parameter.
+ CategoryInfo : NotSpecified: (0:Int32) [New-Mailbox], WLCDManagedMemberExistsException
+ FullyQualifiedErrorId : A5FDB8CC,Microsoft.Exchange.Management.RecipientTasks.NewMailbox
+ PSComputerName : pod51016psh.outlook.com


Turns out that there isn’t a very intuitive way to do this. In order to achieve this, you need to create the shared mailbox with a different alias and then change the WindowsLiveID manually once it is created. For example:

Create a shared mailbox with a different alias.
PS C:\Users\burns_000\Desktop> New-Mailbox -Name "Test Shared Mailbox 2" -Alias test_shared2 -Shared -PrimarySMTPAddress test_shared@cogmotivereports.com
Name Alias ServerName ProhibitSendQuota
---- ----- ---------- -----------------
Test Shared Mailbox 2 test_shared2 db3prd0610mb356 24.75 GB (26,575,110,144 bytes)

You can now see the mailbox and the UPN it has been assigned.
PS C:\Users\burns_000\Desktop> get-mailbox test_shared2 | select userprincipalname
UserPrincipalName
-----------------
test_shared2@cogmotive.onmicrosoft.com

You can also see this in the Exchange Control Panel.

Shared Mailbox with Incorrect UPN

Shared Mailbox with Incorrect UPN

So how do we set the correct login name? With the Set-Mailbox command like this:
PS C:\Users\burns_000\Desktop> set-mailbox test_shared2 -MicrosoftOnlineServicesID test_shared@cogmotivereports.com

And viola, we have the correct UPN.
PS C:\Users\burns_000\Desktop> get-mailbox test_shared2 | select userprincipalname
UserPrincipalName
-----------------
test_shared@cogmotivereports.com

We can also verify this in the Exchange Control Panel.

Shared Mailbox with Correct UPN

Shared Mailbox with Correct UPN

And here are our two shared mailboxes, at different domains:

Two shared mailbox with same alias in different domains

Two shared mailbox with same alias in different domains