When an email from an external sender is sent to hosted quarantine for any reason (i.e. attachment type), notify the sender with reason.
We have a transport rule that moves external email with specific attachment types to hosted quarantine - so we can release them if we need to. We would like to be able to send replies to the sender - asking them to consider re-submitting their email with an acceptable document type such as PDF.
We could do this if we simply blocked the message altogether, but the idea of hosted quarantine is that we can review and release if it is necessary, without involving the original sender.