Outlook notification or notification whenever something is attached

Copper Contributor

Hello, I am wondering if there is an administrative way in Outlook/EXO to cause a custom message or notification whenever an attachment is added to an email.


Reason: We want to drive people to use sharepoint links in emails to share things via email instead of an attachment. 


I do undertand that I can create a reminder notification when Outlook detects that an attachment is forgotten. This is not what I want.


Many Thanks


5 Replies

Hi @Keith Caines 

You could do that with a transport rule. 

Choose if you want it for all recipients or only external ones, choose an attachment size, ( 0KB will filter all kind of attachments. If you choose that, please test it first as some mail signatures have elements considered as attachments ), and decide what should the rule do: Simply notify the sender but allow him to send the message, notify the sender and block the message, etc...




Thank you, but unfortunatly the Attachment size setting is not compatible with the notify Sender.
See error I am getting when saving the rule:

Failed to create the new transport rule
Error executing cmdlet:
|System.ArgumentException|One of the conditions you specified can't be used for rules where you want to notify the sender. Error details: The NotifySender action isn't compatible with 'AttachmentSizeOver' predicate.
Exception of type 'Microsoft.Exchange.Management.PSDirectInvoke.DirectInvokeCmdletExecutionException' was thrown

Hi @Keith Caines,

You're right, my bad, sorry.

What you could do, instead of use a policy tip, use "reject the message and include an explanation". See the screenshot below with a test rule with a custom reject message:




You could also create a DLP rule and specify which kind of attachments would you like to block:



Another idea could be to simply reduce the MaxSendSize in your Exchange environment. But that will need a good previous notification to your users or you'll face a huge support request tickets increase.




@Keith Caines 


Hi All,

I am also trying to add a notification tip for all outbound emails with an attachment to external recipients.  I want the email to be blocked with an override option for the sender.  The purpose is to have the sender review the recipient and attachment for accuracy for DLP and to not send the wrong data to the wrong recipient.  This seems to be basic DLP requirements today.