Exchange Admin MSG/EML blocking rule not applying

Question

We are wanting to block msg and eml attachments from external users. We have tried multiple methods, but none are working. We currently have a rule to block eml and msg message types, but it isn't working when sending from the outlook application. It will work if the sender is sending from the outlook web version. We paid for Microsoft support hours, but they weren't able to solve it either. In message traces, the rule doesn't even show up, but other rules do.

Answer 1

Hi @Jordan Washburn ,

To better understand your problem, could you please provide some details?

1. Do external senders receive NDR after sending from the client side and web side?
2. What kind of messages do recipients in your organization receive? Whether the original attachment is still included?

I created the same rule, and according to my tests, senders who send emails from both the client and the web to internal recipients receive an NDR.

I noticed that the rule you created has a priority of 4, and I suggest you move up the priority to see if the problem can be solved.

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Answer 2

You are going to hate this answer, but I recall from many years ago that is expected as it those message types essentially aren't exposed to the attachment filter in Exchange when sent via the Outlook windows client. I wish I could find the KB article on it, I know I finally found one that explained it.