Posting Notifications About Inactive Mailboxes to Teams

Building on User Mailbox Report

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.

And then I had the idea that maybe it would be good to filter the output to find inactive 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 Office 365 tenants to bring information sourced from applications into Teams and Office 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 in the last 90 days. This is a pretty good indicator of inactivity. I then generated the necessary JSON format payload consumed by Teams and posted the resulting message to the webhook. Here’s the script:

The message as it appears in Teams looks like the message shown in Figure 1:

Inactive Office 365 user information posted to a Teams channel
Figure 1: Inactive Office 365 user information posted to a Teams channel

Remember the Teams Maximum Message Size

There’s nothing earth shattering in the code and there are plenty of similar examples 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.


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

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3 Replies to “Posting Notifications About Inactive Mailboxes to Teams”

  1. One issue I noted with this and I am not sure why is the script returns 15 inactive users and I send them all to teams however Teams only shows the first 10. I have removed information and the image etc to see if its a size issue, but it still only shows 10. Any ideas?

    1. As explained in the post, a post to Teams can be a maximum of 25KB. You’re probably hitting that limit…

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