Comments on: Blocking Attachments based on the File Extension on Microsoft 365

By: ingallspw

ingallspw — Fri, 18 Mar 2022 12:08:56 +0000

Oh here is the summary
Block_hostile_attachments
If the message…
has an attachment with a file extension that matches one of these values: ‘bat’ or ‘exe’ or ‘html’ or ‘htm’ or ‘msi’ or ‘vbs’
Do the following…
reject the message and include the explanation ‘Disallowed File Extension on Attachment’ with the status code: ‘5.7.1’
and Stop processing more rules
Rule comments

Rule mode
Enforce
Additional properties
Sender address matches: Header or envelope
For rule processing errors: Defer
Version: 15.0.1.1

By: ingallspw

ingallspw — Fri, 18 Mar 2022 12:07:32 +0000

For some reason, this only seems to be working on outbound email for us. If a scammer sends an HTML attachment, it makes it through but when anyone internally tries to send on, it blocks it.

By: Tim Shaw

Tim Shaw — Wed, 09 Feb 2022 23:08:56 +0000

really helpful. It is easy to miss the show more button to find this. Thanks for taking the time to share your solution.

By: roe

roe — Tue, 03 Aug 2021 19:03:30 +0000

In reply to Zebra Eyes. Thank You. Very helpful

By: Zebra Eyes

Zebra Eyes — Fri, 30 Jul 2021 19:03:19 +0000

In reply to Nicholas Kulkarni. No, they are still there... click show more on the bottom, and then go back to the drop down and there will be more advance options re-worded.

By: Nicholas Kulkarni

Nicholas Kulkarni — Fri, 16 Jul 2021 09:50:39 +0000

As of 2021 that option is not available in the standard Exchange Admin Centre for Office 365. The only apply this rule if… that mentions attachments is Any Attachments’ content includes… and allows only words in the list. There are no extension options. These extension filtering options are now in Security and need to be edited manually via a script in order to add .htm or .html see http://byronwright.blogspot.com/2017/09/customizing-file-types-for-common.html