Unified Messaging

Managing Unified Messaging Users in Exchange Online

The phone number you entered has already been registered by someone else.

This is the standard error you’ll see in the Exchange admin center when trying to enable Unified Messaging on an extension that already has it enabled.

When a user departs you’d expect that when you change the user mailbox to a shared mailbox and drop the licensing, Unified Messaging should go. However, in Exchange Online the mailbox will still be Unified Messaging (UM) enabled, and hang onto the extension it had.

You probably won’t even notice this until you go to enable UM on another mailbox using that same extension, which leads to the error at the top of this article.

The first challenge is to find the Shared Mailbox that is holding onto the extension. After connecting to Exchange Online in PowerShell, you can run this command:

get-ummailbox | select name, phonenumber | out-gridview

This will show a nice gridview of all your mailboxes and what UM extension they have. You can search/filter this view to find the cuplrit.

If you want to see which of your mailboxes are Shared and have UM enabled, run this command:

Get-Mailbox -RecipientTypeDetails SharedMailbox -ResultSize:Unlimited -filter {umenabled -eq "true"}

Knowing this mailbox, you’d expect it should be easy to turn off UM. This wouldn’t be too much of a problem if you could just disable UM like you can on a normal mailbox, but in Exchange admin center this isn’t an option at all when it’s a shared mailbox.

Trying to disable UM via PowerShell with the ‘Disable-UMMailbox’ command also won’t work, as you’ll get a license error:

License validation error: the action 'Disable-UMMailbox', 'Identity', can't be performed on the user 'Test User'
 with license 'BPOS_S_Standard'.
     + CategoryInfo          : NotSpecified: (:) [Disable-UMMailbox], RuleValidationException
     + FullyQualifiedErrorId : [Server=SYXPR01MB1901,RequestId=dfc62192-8270-4a65-b582-c7f327d6e7e2,TimeStamp=15/10/201
    9 6:24:33 AM] [FailureCategory=Cmdlet-RuleValidationException] DDB44050,Microsoft.Exchange.Management.Tasks.UM.Dis
     + PSComputerName        : outlook.office365.com

To fix this, you could use the Exchange admin center GUI along with the Microsoft 365 Portal, but it’s easier to run all the steps required via PowerShell:

First apply a license to the shared mailbox account that includes Exchange Online. You can see what licenses are available to you with this PowerShell command used by the MsolService cmdlet:


Then, apply a license with this command against the shared mailbox and the AccountSkuID from the previous command:

Set-MsolUserLicense -UserPrincipalName "UPN OF SHARED MAILBOX" -AddLicenses "tenant:licensename"

Once applied, you’ll then need to change the mailbox to a Regular mailbox rather than Shared:

Set-Mailbox "UPN OF SHARED MAILBOX" -Type Regular

After a while, Unified Messaging may drop off by itself if you allocated a license that doesn’t support it (such as Exchange Online Plan 1 or Exchange Online Kiosk, or you can force it off with this command:

Disable-UMMailbox -Identity  "UPN OF SHARED MAILBOX"

Finally you can now enable UM on that other mailbox that was getting the error on the extension being in use. Easily done via the Exchange admin center GUI.

Two last steps are then to reverse what you did – take the license away from the shared mailbox, and make it a shared mailbox again:

Set-MsolUserLicense -UserPrincipalName "UPN OF SHARED MAILBOX" -RemoveLicenses "tenant:licensename"

Set-Mailbox "UPN OF SHARED MAILBOX" -Type Shared

Converting a user mailbox to shared in Exchange Online Hybrid

This is a useful process a lot of companies follow when an employee departs: Instead of deleting the mailbox, or continue to leave the mailbox in place and pay for licensing, it’s possible to instead set it as a shared mailbox and keep the data there for free.

There are some catches to this, such as the maximum amount of data is 50gb. You also can’t delete the user’s account, but it can be disabled and moved.

Setting the mailbox from User to Shared in Exchange Online is easy (from docs.microsoft.com):

In the admin center, go to the Users > Active users page.

Choose the user whose mailbox you want to convert.

In the right pane, choose Mail. Under More actions, choose Convert to shared mailbox.

…but there’s two tricks I’ve found when doing this in a hybrid environment. First, docs.microsoft.com says to update the status of the mailbox for Exchange On-Premises:

If this shared mailbox is in a hybrid environment, we strongly recommend (almost require!) that you move the user mailbox back to on-premises, convert the user mailbox to a shared mailbox, and then move the shared mailbox back to the cloud.

That’s a tedious process to do just to make it shared. As they point out, you can change some AD attributes locally to get around this, but there’s still some scenarios where it might get set back as a user, have no license, and end up getting deleted.

This other article on support.microsoft.com however, mentions the main way of getting around this: by setting the account’s msExchRemoteRecipientType and msExchRemoteRecipientTypeDetails attributes to the corresponding values that would match it’s state in Exchange Online:

Set-ADUser -Identity ((Get-Recipient PrimarySmtpAddress).samaccountname) -Replace @{msExchRemoteRecipientType=100;msExchRecipientTypeDetails=34359738368}

This 1 line command will set the attributes correctly, you can check via PowerShell or the Exchange Management Console to see that the mailbox will now show as ‘Shared’.

The other problem I’ve seen is if a mailbox is Unified Messaging (UM) Enabled, and converted to Shared. You’d think that it would either just lose it’s UM status, or let you configure the UM settings after the fact; but neither are correct. If it’s holding onto an extension number as part of UM, even in it’s Shared Mailbox state it will continue to hold it, and block any other account from using the extension in the future.

To get around this issue, the account will need to both be changed back to a user account from shared, and given a license that supports UM. If you try to disable UM on the account with either of these requirements, you’ll see an error like these:

User testuser@domain.com is already disabled for Unified Messaging.

License validation error: the action ‘Disable-UMMailbox’, ‘Identity’, can’t be performed on the user ‘Test User’ with license ‘BPOS_S_Standard’.

With all of the above, changing a user to a departed mailbox in a hybrid environment with Unified Messaging should be:

  1. Disable Unified Messaging on the user
  2. Set the attributes of the AD account as shared
  3. Set the Exchange Online mailbox as shared

It should work well if you do things in the right order, but it’s easy to not be aware of this and get things into a mess.

There’s also the scenario where you might create an account, give it Office 365 licenses and have a mailbox automatically created before you did it on-premises, or used Exchange On-premises to create the mailbox remotely.

You can fix that by using this script from Adaxes (doesn’t need their software!) which will tell on-premises Exchange about the mailbox and create the record.

I’ve come across another blog that goes into some of this http://jetzemellema.blogspot.com/2016/02/convert-user-mailbox-to-shared-in.html but I haven’t needed to change the license status, but it’s worth mentioning in case there’s a scenario you hit where you do.

Lync Issue – Deskphone Answers When Delegate Picks Up Call Via Headset


Sorry I couldn’t make that headline any shorter! This issue was bugging us for a while, and finally found the answer.



Lync 2010 with Enterprise Voice. User A sets up User B as a Delegate for calls, and sets their phone to forward or simultaneously ring to User B via the Delegates option as per this screenshot:


User B has both a Lync desk phone tethered to their computer via USB, and a headset plugged into their computer. User B answers the call either by clicking on the incoming call toast, or pressing their headset button. Even though their Lync client is set to use the headset as the default device, the desk phone answers the call in speaker mode.


This seems rather weird, especially if you call User B direct they can answer the call straight to their headset. We spent quite some time testing this, trying different options, upgrading firmware, uninstalling/reinstalling anything we could think of until finally I found this technet post: http://social.technet.microsoft.com/Forums/lync/en-US/6e1f9d63-a403-4589-868f-1bd6a1a5e440/lync-delegate-bug?prof=required – scroll down to the last post by William Curley which has this exact problem.

The annoying part is that he claims that Microsoft classify this scenario as a ‘not supported scenario’. The best fix for this is to use Team-Call Group instead of Delegate, but you do lose the ability for Delegates to manage User A’s calls and make meetings on their behalf. This apparently applies to Lync 2013 also, but I don’t have that running to verify.

Lync also won’t like it if you set User A and User B to be delegates for each other, weird things start happening with who’s voicemail the call goes to.

The safest suggestion I have is to just avoid the Delegate option altogether if you use Lync with Enterprise Voice.

I hope this information saves someone a lot of time!

Update 17/10/2013: It looks like Microsoft have released a patch to fix this. http://support.microsoft.com/kb/2889646/en-au has the long title of “PSTN call is routed to an Aries telephone in speaker mode when a delegate answers the call in Lync 2010 by using a USB headset” which fits this exact scenario. It’s a part of the cumulative update for Lync 2010 October 2013 which is available for download, but not in the update catalogue for WSUS servers yet.

Exchange 2010 Unified Messaging – Unrecognised Voicemail Extension


I had an issue where a particular user’s voicemail on Exchange 2010 wasn’t working. When they called the voicemail number, they were asked “To access your mailbox, please enter the extension” rather than being greeted with their name and messages. The user was on Lync 2010, and Unified Messaging was enabled on their account with the matching extension number. Also, when dialing voicemail and trying to enter the extension number just met the message ‘XXX isn’t a valid mailbox’.

Disabling and re-enabling Unified Messaging made no difference. I was rather confident this was an Exchange/Unified Messaging issue, so I had the idea of checking ADSI edit to see if UM was properly enabled.

Checking the attribute “msExchUMEnabledFlags” found the issue. When a user has UM enabled, the value of this field should be 831, or 830 when disabled. I’ve come across this issue before, where it’s the wrong value and needs to be changed, but this was the first time I’d come across it as being 832.

Never a good sign when you google something, and you get zero results:


Changing the Attribute value back to 831 instantly fixed the issue, didn’t even require disabling and re-enabling Unified Messaging. If all else fails, change the value back to 830, refresh your Exchange Management Console and the user should show as being disabled for Unified Messaging, then re-enable as you normally would.

Hope this helps anyone else who comes across a similar issue.