KB ID 0001544

Problem

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;

Solution

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”.

Scroll down.

Tick: Stop processing more rules.

Save.

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;

[box]

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

[/box]

Related Articles, References, Credits, or External Links

NA