Configuring Skype for Business and Office 365 Unified Messaging for Voicemail is a fairly simple task. Of course no task should be undocumented, so here goes.


On premise Skype for Business 2015 deployment
Mail delivered via Office 365
On premise users synchronised back to Office 365 via DirSync

NOTE: UM connectivity, in this case is done via Federation to Office 365. So it goes without saying that a working Edge infrastructure is required. Also Federation needs to be enabled (and working)

First we will configure the Skype for Business Front End Pool

From the Skype Front End Server
1. Ensure that Federation is enabled for the Edge Configuration (Federation needs to be enabled in the Topology). Confirm by the following cmdlet:-



To change AccessEdgeConfiguration:-

Set-CsAccessEdgeConfiguration -enablepartnerdiscovery $true -UseDnsSrvRouting -AllowFederatedUsers 1

NOTE Partner discovery may be either enabled or disabled.

2. Adding O365 as a hosting provider for UM

New-CsHostingProvider -Identity “Exchange Online” -Enabled $True -EnabledSharedAddressSpace $True -HostsOCSUsers $False -ProxyFqdn “exap.um.outlook.com” -IsLocal $False -VerificationLevel UseSourceVerification


3. Make sure these changes have been replicated (don’t continue until it has!)

Force Replication with:


Confirm with Replication Successfully completed:


check replication

4. We now need to add the Hosted Voicemail policy, The Office 365 Tenant Name is required for this. The policy is added with the following cmdlet:

NOTE “CloudUM” in my case is the name I gave the on premise UM Policy

New-CsHostedVoicemailPolicy -identity CloudUMPolicy -Destination exap.um.outlook.com -Description “Office 365 Voicemail” -Organization “tenantname.onmicrosoft.com


TIP: To find the Organization name login to O365 Admin Portal. Don’t use the same Tennant name as the on premise SIP domain as that will resolve to on premise and, of course, for voicemail it needs to resolve to O365

The Organization Name is also the *Default Domain as defined in the Admin Center in the Company Profile page

Skype for Business Office 365 Unified Messaging

Skype for Business Office 365 Unified Messaging

Next, we need to configure Office 365

From the Office 365 Portal

  1. Navigate to Unified Messaging (Office 365 Admin Center – Exchange – Unified Messaging

2. Add a new UM Dial Plan by clicking on the +

UM Dial Plan

3. Complete the New UM Dial Plan Page as per your requirements and click Save

Office 365 Dial Plan
 4. To assign the Subscriber access number, edit the UM Dial Plan you just created.
UM Edit
5. Click on configure
Subscriber access configure
6. Select Outlook Voice Access and add the DDI\DID assigned to the ExUmContact on premise as DisplayNumber (see next step)

Next we head back to Skype for Business

  1. Create the UM Contact

New-CsExUmContact -displaynumber +613456789 –sipaddress SIP:EX_UM_365_SA@ucsorted.com -registrarpool pool01.ucsorted.com -ou “OU=IT,OU=UCSorted,DC=com”

TIP: I often come across a request to change Subscriber Access number, use Set-ExUmContact to change it if you need too.

NOTE: By specifying the “DisplayNumber” the LineUri is also set (I know its odd)


2. Assign the Hosted Voicemail Policy to the EX UM Contact

Grant-cshostedvoicemailpolicy –identity “CN={f169db8b-….DC=au” –policyname CloudUMPolicy

TIP: I am not very fond of copying the identity in this manner. Since I have added only the 1 exumcontact I just do the following:-

Get-CsExUmContact | Grant-CsHostedVoicemailPolicy -PolicyName CloudUMPolicy

Then we switch to Exchange Online PowerShell

TIP: Use the following script to connect to EOL:

$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection

Import-PSSession $Session

Exchange Online


Set-UMmailboxpolicy -identity “Office 365 UM Default Policy” -SourceForestPolicy “OnPremUMPolicy”

TIP: The identity is that of the Office 365 UM Mailbox Policy (not the UM Dial Plan)

The following step only applies if UM is already deployed on premise and this UM deployment is part of migrating UM to O365. This is done from the on premise exchange environment.

Set-UMmailboxpolicy -identity “On Premise UM Policy” -SourceForestPolicy “CloudUMPolicy”

Finally, time to configure users


You cannot have a spilt setup where UM is in O365 and the user mailbox is on premise or vice versa.

2 steps are required for enabling users for UM in O365:-

  1. From SkypefB – Grant the user the Hosted Voicemail Policy and enable the user for Hosted Voicemail
  2. From O365 – Enable the user for UM

Within Skype for Business 2015 PowerShell

Grant-cshostedvoicemailpolicy –identity “paulb” –policyname CloudUMPolicy

get-csuser –identity “paulb”

Set-csuser –identity “paulb” –hostedvoicemail $true

Within O365 Exchange Admin Center

Navigate to Recipients (Office 365 Admin Centre – Exchange – Recipients)

Find the user you would like to enable for UM and click Enable

O365 Recipients

Browse for the O365 UM Mailbox Policy and click next

UM Mailbox Policy

Provide the required extension number and PIN settings, click Finish to complete.

UM Extension

Of course synchronization by way of DirSync is required to ensure that the account is enabled for unified messaging.