Microsoft Defender for Office 365: add Anti-Malware extensions

Microsoft Defender Office 365

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Within Microsoft Defender for Office 365 it is possible to activate Anti-Malware protection to avoid attacks based on potentially dangerous attachments.

By default, different formats are made available but not all and above all not all those that over time appear to be invalid for the various IT departments.

To add new extensions to the shopping list, it is not possible to use the UI but it is necessary to use PowerShell with the following syntax:

$FileTypesAdd = Get-MalwareFilterPolicy -Identity “Anti-Malware Policy” | select -Expand FileTypes

$FileTypesAdd += “xslm”,”pptm”
Set-MalwareFilterPolicy -Identity “Anti-Malware Policy” -EnableFileFilter $true -FileTypes $FileTypesAdd

NB: The Identity value changes by your policy name.

The new extensions will not be visible within the web portal but it will be possible to query the list using the following PowerShell command: Get-MalwareFilterPolicy -Identity “Anti-Malware Policy”| select -Expand FileTypes

Once applied, the rule will be applied to internal and external traffic returning a message like the following.


In a few steps you can go and customize Defender for Office 365 Anti-Malware rules, so as to increase the security of your mail platform.