“Server error Category A is not supported” message when enabling Microsoft Defender for Office 365 in the Microsoft Sentinel Connector

Recently, a few of us were confused about an error message that exhibited itself when attempting to enable the Microsoft Defender for Office 365 option in the Microsoft 365 Defender connector for Microsoft Sentinel. Never experiencing something like this yourself, makes it even more difficult to troubleshoot. You know the scenario – user or customer says something’s not working – you try it you say, “hey, works for me.”

After a bit of back-and-forth troubleshooting, the customer resolved this through trial-and-error, and I wanted to share this particular resolution because the issue has cropped up recently more than once.

The issue was that the preview features option for Microsoft 365 Defender wasn’t turned on. After enabling it, everything started working.

To enable it:

  1. In the navigation pane at security.microsoft.com, select Settings.
  2. Select Microsoft 365 Defender.
  3. Select Preview features > Turn on preview features.
  4. Select Save.


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