Blocking specific file types as attachment in a Transport rule

Question

Blocking specific file types as attachment in a Transport rule

Bühler Gabriel 41

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 3,726 Reputation points Microsoft Vendor

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

Hi @Bühler Gabriel ,

Just checking in to see if above information was helpful. Please let us know if you would like further assistance.

If the question has been answered, please accept the helpful replies as answers, this will make answer searching in the forum easier and be beneficial to other community members as well.
Jame Xu-MSFT 3,726 Reputation points Microsoft Vendor

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

Hi, I'm here to confirm with you if your issue has been resolved. If the problem is successfully solved, you can share your solution and mark them or the helpful reply as answer, this will make answer searching in the forum easier and be beneficial to other community members as well.

Jame Xu-MSFT 3,726 Reputation points Microsoft Vendor

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

Hi @Bühler Gabriel ,

Just checking in to see if above information was helpful. Please let us know if you would like further assistance.

If the question has been answered, please accept the helpful replies as answers, this will make answer searching in the forum easier and be beneficial to other community members as well.
Jame Xu-MSFT 3,726 Reputation points Microsoft Vendor

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

Hi, I'm here to confirm with you if your issue has been resolved. If the problem is successfully solved, you can share your solution and mark them or the helpful reply as answer, this will make answer searching in the forum easier and be beneficial to other community members as well.

Answer 1

Vasil Michev 66,781 MVP

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.

Bühler Gabriel 41 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 66,781 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

Blocking specific file types as attachment in a Transport rule

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