How to Post Notifications About Unused Mailboxes to Teams

Extracting Unused Mailbox Information from Mailbox Diagnostics

Recently, I posted a Petri.com article to report the availability of some new properties in the Export-MailboxDiagnosticLogs cmdlet. The properties record different kinds of mailbox activity, and I included a script to generate a report based on the properties. The output is a CSV file that can be opened in Excel or imported in Power BI. All is well.

I then had the idea that maybe it would be good to filter the output to find unused mailboxes and post that information to a Teams channel as a form of proactive notification to administrators. Not having endless time, I browsed the web to find a PowerShell script to serve as a starting point and found one that reports inactive Active Directory accounts. That’s not a long way from what I wanted to do, so I grabbed the code and edited it to fit my purpose.

Using Incoming Webhook Connector to Post to Teams

Posting messages to a Teams channel is easily done using the incoming webhook connector, one of the standard connectors available to all Microsoft 365 tenants to bring information sourced from applications into Teams and Microsoft 365 Groups. When you configure the connector for a channel, you get a webhook (unique identifier) to post messages to the channel.

I then filtered the set of mailboxes I created in the table generated by the previous script (see link above) to find mailboxes with no email activity over the last 90 days. If a mailbox has no activity in three months, it’s a good indicator that it is an unused mailbox. I then generate the necessary JSON format payload consumed by Teams and post the resulting message reporting the unused mailboxes to the webhook. Here’s the script:

# Script uses some code from https://www.thelazyadministrator.com/2018/12/11/post-inactive-users-as-a-microsoft-teams-message-with-powershell/

$WebHook = "https://outlook.office.com/webhook/42f6d6b0-c191-496d-85b4-bfd6e63e230b@b662313f-14fc-43a2-9a7a-d2e27f4f3478/IncomingWebhook/62c92a65258a416b90e969980ae4ebb1/eff4cd58-1bb8-4899-94de-795f656b4a18"

$InactiveTable = New-Object 'System.Collections.Generic.List[System.Object]'
$PersonImage = "https://img.icons8.com/cotton/2x/gender-neutral-user--v1.png"
$Today = (Get-Date)
ForEach ($R in $Report) {
   $DaysSinceLastEmail = ((New-TimeSpan –Start $R.LastEmail –End $Today).Days)
   If ($DaysSinceLastEmail -gt 90) {
   $UserData = @{
     ActivityTitle = "$($R.Mailbox)"
     ActivitySubTitle = "-----------------------------------------------"
     ActivityText = "$($R.Mailbox)'s last email activity was on $($R.LastEmail)"
     ActivityImage = $PersonImage
     Facts = @(
        @{	
	  name  = 'Mailbox:'
	  value = $R.Mailbox 	},
	@{
	  name  = 'Last Email activity:'
	  value = $R.LastEmail 	},
	@{
	  name  = 'Days since last activity:'
	  value = $DaysSinceLastEmail	},
	@{
	  name  = 'Last active time (unreliable):'
	  value = $R.LastActive 	} )
	}
   $InactiveTable.Add($UserData)
   Write-Host $R.Mailbox $R.LastEmail $DaysSince }}

$Body = ConvertTo-Json -Depth 8 @{
	Title = "Possibly Inactive Office 365 Users"
	Text  = "There are $($InactiveTable.Count) users with no detected email activity for 90 days or more"
	Sections = $InactiveTable }

# Only post if we have less than 25 items
If ($InactiveTable.Count -lt 25) {
    Write-Host "Posting inactive account information to Teams" -ForegroundColor Yellow
    Invoke-RestMethod -uri $WebHook -Method Post -body $body -ContentType 'application/json' }
Else {
    Write-Host "Too many (" $InactiveTable.Count ") inactive accounts found to post to Teams... Spread the bad news another way" }

The message posted to Teams looks like the example shown in Figure 1:

Remember the Teams Maximum Message Size

There’s nothing earth shattering in the code and plenty of similar examples are available online (such is the joy of PowerShell). What is important to note when you post to Teams is that the message is limited to a maximum size of 25 KB. If your message exceeds the limit, Teams responds with a HTTP 413 error similar to:

Microsoft Teams endpoint returned HTTP error 413 with ContextId tcid=982653230009892365,server=DB3PEPF00000461,cv=4LrmcZGylkmtD0uEToTT2g.0.

In my case, it seemed like the error happened if more than 28 or so items were in the list of reported accounts. This will obviously vary depending on how much data you try to post for each item.

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For more information about using Teams and Microsoft 365 Groups with connectors, read the Office 365 for IT Pros eBook.