Deny email attachments for certain users in mail flow?

[Dany Mcdonald]

Hello,

First, sorry for the neophyte question, I do not manage mail flow but I am task with a project and need to ask.

I have to control how a certain subnet access internet and have managed to deny any types of file upload through our core firewall for any destination except for O365.

So can I deny attachments in mail flow for targeted users (around 100) in that subnet for O365 in mail flow? Denying upload of files to every O365 apps would also be important. I dont want to deny the entire domain...

It's pretty complicated in firewall rules and mail flow would be the easy and logical way.

Thank you for help,

Dany

[#2]

You can certainly create mail flow rules to reject messages containing attachments and addressed to certain recipients. There is no way to tie this to your internal subnet though, so you should base the rule on some other criteria (user's email addresses for example).

There is no mail flow rule action to "strip" attachments though, you will have to block the message delivery altogether.

[#3]

Hello Vasil,

Good news!

By subnet I meant a bunch of users... Any chances you could point me toward online info?

I did look for mail flow how to's but did not find.

Thank you for your time!

Dany

[#4]

The documentation on Mail flow rules is here: https://technet.microsoft.com/en-us/library/jj919238(v=exchg.150).aspx

In your case you can use the "recipient is" clause to scope the rule down to those users, and also include the "sender is external" clause. If you want to block any messages with attachments, simply use the "attachment size is greater than 1KB" or similar. More examples here: https://technet.microsoft.com/en-us/library/jj919236(v=exchg.150).aspx

[#5]

Thank you Vasil, it's appreciated.

Dany