Category Archives: Office 365

Ghost Mailusers

We had an odd case today that Msft support hasn’t fixed yet, but in case someone googles the error and finds this, I did find a workaround.

We had a MailUser object that was inactive (soft deleted), but couldn’t be permanently deleted using

Remove-MailUser -PermanentlyDelete -Identity $mailuser.ExternalDirectoryObjectId

The resulting error was:

This mail enabled user cannot be permanently deleted since there is a user associated with this mail enabled user in Azure Active Directory. You will first need to delete the user in Azure Active
Directory. Please refer to documentation for more details.

However, nothing was found in AzureAD (or deleted users/recycle bin), and nothing was present in our on-prem AD.

This user was deleted a long time ago, and now being rehired….but account creation was being blocked because the mail user was still claiming the email address of this user.

After some messing around, and not patiently waiting for Msft 1st line support to delete this corrupted MailUser, I discovered the RecalculateInactiveMailUser switch in the set-MailUser command.

Normally, you can’t modify the primary smtp / aliases of a soft deleted mailuser or mailbox….BUT, for some reason, if you supply RecalculateInactiveMailUser you can. So:

Set-MailUser -Identity $mailuser.ExternalDirectoryObjectId -EmailAddresses $newProxies -RecalculateInactiveMailUser

Worked fine! While

Set-MailUser -Identity $mailuser.ExternalDirectoryObjectId -EmailAddresses $newProxies

Failed with

The operation couldn’t be performed because object ‘270fc89f-0424-42d2-8f54-25796f74457b’ couldn’t be found on ‘DB8PR02A05DC001.EURPR02A005.PROD.OUTLOOK.COM’.

Inviting an external user to a PowerApp programmatically

Another week, another use case for Managed Identities in Automation Accounts!

The scenario today concerns a PowerApp and connected resources that should be shared with external identities, automatically of course. For each user this requires a guest account in the host / resource tenant, and a license. The license can be applied in the home tenant of the guest, or in your tenant.

Key points:

  1. Runbook that invites a user and adds the resulting guest account to a security group
  2. Security group gives access to the PowerApp and underlying (SpO) resources, and uses Group Based Licensing to license the guest for PowerApps and Sharepoint Online
  3. Logic App that is triggered by the PowerApp (trigger on create item in a sharepoint list), and starts the runbook
  4. When the invited user (guest) redeems the invitation, they are directed to a Sharepoint page first so Sharepoint syncs their profile. Otherwise, the PowerApp will not have access to any lists in Sharepoint Online as Guests are not synced to SpO until they access SpO directly.

I may demo the PowerApp, Logic App and Sharepoint lists at some point, but the main thing I wanted to share today is the Azure Runbook that creates the Guest invitation and adds the Guest to a security group using the Managed Identity of the Automation account, instead of service accounts or other pre-2021 solutions:

Redirecting anything to Onedrive for Business

A while ago I wrote a script that can mount Teams Libraries and then redirect any local folder to them.

In many situations, this solution is a little overkill though, so I’ve also created a second version which simply allows you to redirect any local folder (including variable paths!) to any location in a user’s Onedrive folder.

The configuration is set through the registry, an example file is included.

It can be used as a onetimer or as logonscript, and it can also be used to migrate existing content or create hard links for specific local appdata folders.

Exchange Hybrid lockdown to O365 IP’s only

With the recent Exchange vulnerabilities comes a moment to reflect on further ways to reduce the attach surface of Exchange Servers.

Many organizations still host an Exchange Server solely to maintain a hybrid connectivity link to Office 365. The server therefore has to be publicly accessible, but only to Microsoft. Often this is not the case.

If you don’t have a professional firewall to restrict traffic to only that coming from Microsoft, you can also do so at the IIS level. Microsoft publishes a list of IP’s they use here:

We can then take that source address data and add each IP in it to an Allow entry at the global level in IIS using PowerShell:

$allRanges = @("fe80::946:a60c:3d5:ec11%3","","::1")
$o365IPs = Invoke-RestMethod -Method GET -UseBasicParsing -Uri "" 
$o365IPs | % {$_.ips | %{if($allRanges -notcontains $_){$allRanges += $_}}}
$allRanges | % {
        $payLoad = @{ipAddress=$_.Split("/")[0];allowed="true";subnetMask=$(([ipaddress]([double]4294967296-(1-shl32-$($_.Split("/")[1])))).IPAddressToString);}
        $payLoad = @{ipAddress=$_;allowed="true";}
    try{$null = Add-WebConfigurationProperty  -Filter 'system.webServer/security/ipSecurity' -PSPath "IIS:\" -Name "." -Value $payLoad -ErrorAction SilentlyContinue}catch{$Null}

Finally, set IIS’s IP Address and Domain restriction mode to Deny:

note: you can add additional ranges to $allRanges as needed for internal management, monitoring etc.