Office 365: Stop One User Sending Attachments

KB ID 0001544


If you have one, (or more) users and you want to BLOCK those users from sending ANY email attachments, here’s how to do it;


Log into your Office 365 tenancy with administrative access > Admin > Admin Centers > Exchange Admin > Mail Flow > Rules > Add > Filter Message By Size.

Name: Give it a sensible name.
Apply This Rule If: The message size is greater than or equal to = 1.00 KB (we will change this in a minute!)
The Sender Is: Add the user(s) in question.
Do The Following: Reject the message with the explanation = “Enter some sensible text”.

O365 Block Attachments for One User

Scroll down.

Tick: Stop processing more rules.


Stop Processing Rules

Now this blocks all attachments over 1KB (1024 bytes), but this still lets a user send a smaller attachment! The ONLY way to fix that, is to drop the limit using PowerShell.

Connect to Office 365 Exchange PowerShell

Then use the following syntax;

Set-TransportRule -Identity "Name" -AttachemtnSizeOver 1B

O365 Block All Atachments from One User


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Author: PeteLong

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