Converting Dynamic Distribution Lists to Microsoft 365 Groups and Teams

Creating Teams from Exchange Online DDLs

After writing about the recent revamp of Exchange Online dynamic distribution lists, I was asked if it was possible to create a team from the membership of a dynamic distribution list. The answer is that the steps are straightforward to create a static Microsoft 365 group. Things get more complicated if you contemplate using a dynamic Microsoft 365 group.

Available in both Exchange Online and Exchange Server, dynamic distribution lists are very powerful. That is, if the organization directory is well-maintained with details about people, job titles, department names, offices, country, and so on. The membership of dynamic distribution lists can include any kind of mail-enabled recipient, including other groups. And that’s the first challenge to face: the Microsoft 365 groups used by Teams support a flat membership (no nested groups) composed solely of accounts belonging to the host organization (members and guests): only user mailboxes can migrate to become members of a target Microsoft 365 group.

The second challenge comes into play if you decide that the target Microsoft 365 group should have dynamic membership. The issue here is that dynamic distribution lists use filters executed against Exchange Online’s directory while dynamic Microsoft 365 groups use filters based on Azure AD. Different filters, different syntax, and different properties. More on this later.

Converting a Dynamic Distribution List to a Team with Static Membership

Starting with the simple issue of finding the members of a dynamic distribution list and using this information to create a new Microsoft 365 group, the steps are straightforward:

• Identify the source dynamic distribution list.
• Get the members of the dynamic distribution list and throw away any that can’t be members of a Microsoft 365 group.
• Check that the owner of the source dynamic distribution list is a valid mailbox.
• Create the new Microsoft 365 group using properties like name and description inherited from the source dynamic distribution group. The person who manages the dynamic distribution list becomes the owner of the Microsoft 365 group.
• Add the members to the new Microsoft 365 group to the membership.
• Team-enabled the new Microsoft 365 group.

The script I created is available in GitHub. Normal caveats apply: the code works but it doesn’t have much error checking. It’s there to prove a principle, not be an off-the-shelf solution.

Finding the Source

Multiple ways exist to identify a source dynamic distribution list. This example prompts the user to select one. The code could become a lot more complex to allow the user to make a mistake and select from a numbered list, and so on, but for the purpose of the example all we want is the object identifier for a valid dynamic distribution list:

$InputDDL = Read-Host "Enter the name of the Dynamic Distribution List to convert to a Microsoft 365 Group"
[array]$SourceDDL = Get-DynamicDistributionGroup -Identity $InputDDL -ErrorAction SilentlyContinue

If (!($SourceDDL)) {Write-Host ("Sorry! We can't find the {0} dynamic distribution list" -f $InputDDL); break}
If ($SourceDDL.Count -gt 1) {
   CLS
   Write-Host "We found multiple matching dynamic distribution lists"
   Write-Host "-----------------------------------------------------"
   Write-Host " "
   $SourceDDL | Format-Table DisplayName, Alias, PrimarySMTPAddress
   Write-Host " "
   Write-Host "Please try again..."; break }

[string]$SourceDDLId = $SourceDDL.ExternalDirectoryObjectId

Two methods exist to return the membership of the dynamic distribution list:

• Run Get-Recipient using the filter stored in the dynamic distribution list.
• Use the new Get-DynamicDistributionGroupMember cmdlet.

The first method resolves against the Exchange directory and its results are up to date. The second fetches membership data as at the last time Exchange processed the list (more information here). After retrieving the membership using the chosen method, we apply a filter to extract mailboxes.

# Now that we have a source DDL, let's get its membership
[array]$SourceMembers = Get-Recipient -RecipientPreviewFilter (Get-DynamicDistributionGroup -Identity $SourceDDLId).RecipientFilter
# could also be 
# [array]$SourceMembers = Get-DynamicDistributionGroupMember -Identity $SourceDDL.Id
# Throw away anything but user mailboxes because that's all a Microsoft 365 group supports
[array]$ValidMembers = $SourceMembers | ? {$_.RecipientTypeDetails -eq "UserMailbox"}

The next piece of code establishes the owner of the new group. Microsoft 365 groups must have an owner, so if the ManagedBy property of the source list results in an invalid result (for instance, it’s empty), we need to assign ownership to a default account. One way of doing this is to find the set of Exchange administrators for the organization and select one of them, which is done here using the Get-MgDirectoryRoleMember cmdlet from the Microsoft Graph PowerShell SDK and filtering out any service principals assigned the Exchange administrator role. You could simplify the script by hardcoding a default group member.

# We've got to assign an owner to the new Microsoft 365 group, so we need to have a default in case the source DDL doesn't have an owner
# Find the set of accounts that are Exchange admins (you can also use Get-AzureADDirectoryRoleMember here)
[array]$ExoAdmins = Get-MgDirectoryRoleMember -DirectoryRoleId "53add08e-5b0c-4276-a582-9ce02fb6c947" | Select Id, AdditionalProperties 
# Throw away any service principals which might have the Exchange Admin role
$ExoAdmins = $ExoAdmins | ? {$_.AdditionalProperties.'@odata.type' -eq '#microsoft.graph.user'} | Select -ExpandProperty Id
# Select the first and use them as the default owner
$ExoDefaultAdmin = Get-MgUser -UserId $ExoAdmins[0] | Select -ExpandProperty UserPrincipalName
# Check that the group owner is a mailbox
$GroupOwner = Get-ExoMailbox -Identity $SourceDDL.Managedby -ErrorAction SilentlyContinue
# If it's null or something weird like a shared mailbox, use the default owner
If (($GroupOwner -eq $Null) -or ($GroupOwner.RecipientTypeDetails -ne "UserMailbox")) {
   $GroupOwner = $ExoDefaultAdmin }
Else {
   $GroupOwner = $GroupOwner.PrimarySmtpAddress
  }

# Populate other group properties
$AliasDDL = $SourceDDL.Alias + "M365"
$GroupDisplayName = $SourceDDL.DisplayName + " (Group)"

Creating the New Group and Team

With everything ready, we can go ahead and create the new Microsoft 365 Group, add the members, and team-enable the group. All the members can be added with a single Add-UnifiedGroupLinks command because we have an array of email addresses. Exchange processes each item in the array and adds it as a member.

# Create the new Microsoft 365 Group
Write-Host "Creating the new Microsoft 365 group..."
$Description = "Created from the " + $SourceDDL.DisplayName + " dynamic distribution list on " + (Get-Date -Format g)
$NewGroup = New-UnifiedGroup -DisplayName $GroupDisplayName –AccessType Private -Alias $AliasDDL -RequireSenderAuthenticationEnabled $True -Owner $SourceDDL.ManagedBy -AutoSubscribeNewMembers -Notes $Description
# Add the members to the group
Write-Host "Adding members from the dynamic distribution list to the Microsoft 365 group..."
Add-UnifiedGroupLinks -Identity $NewGroup.ExternalDirectoryObjectId -LinkType Members -Links $ValidMembers.PrimarySmtpAddress
Write-Host "Enabing Microsoft Teams for the Microsoft 365 group..."
New-Team -Group $NewGroup.ExternalDirectoryObjectId

The code doesn’t add a sensitivity label, so if you use these to apply container settings to groups and teams, you should add the label when creating the new group by passing the identifier for the selected label in the SensitivityLabel parameter.

That’s it. We have a new team built from the membership of a dynamic distribution list. The code is straightforward and works without a hitch, but if we throw dynamic membership for the Microsoft 365 group/team into the equation, things become much more complex. I’ll cover that subject in another post.

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