Blocking specific file types as attachment in a Transport rule

Bühler Gabriel 81

Hello Everyone

Is there a way to create a specific Transport rule that blocks all incoming E-Mails that contain HTML-Files as attachments?

I can adjust my Malware-Policies to block these kinds of E-Mails for outgoing E-Mails, and I can block a specific set up list of file-types, but I would like to add additional file types to this transport rule.

Thank you for your Help.

Kind regards,

Gabe

Jame Xu-MSFT 4,176 Reputation points

2023-03-13T06:08:44.98+00:00

Hi @Bühler Gabriel ,

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Jame Xu-MSFT 4,176 Reputation points

2023-03-28T09:37:34.5066667+00:00

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1 answer

Vasil Michev 109.7K Reputation points MVP

2023-03-09T15:17:13.99+00:00

Sure, you should be able to use the AttachmentExtensionMatchesWords condition, as detailed for example here: https://learn.microsoft.com/en-us/exchange/security-and-compliance/mail-flow-rules/inspect-message-attachments#inspect-the-file-properties-of-attachments

Though the common attachment filter under Malware policies is probably a better place to enforce this.
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Bühler Gabriel 81 Reputation points

2023-03-09T16:17:31.7933333+00:00

Hello Vasil

Thank you for your help. Can I also specify placeholders for the Matching word (like *.html)?

I was testing the malware filter, but It unfortunately only blocked outgoing E-Mails...is there a possibility to block incoming E-Mails as well? I was not able to enter in external domains.

Kind regards,

Gabe

Vasil Michev 109.7K Reputation points MVP

2023-03-09T17:00:04.0166667+00:00

For that you can use the AttachmentNameMatchesPatterns condition.

But take a look at the Common attachment filter functionality: https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/anti-malware-protection-about?view=o365-worldwide#anti-malware-policies
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