Incoming Documents has a lot of potential and the outlook integration is fantastic. The only issue is that it is possible for multiple people to get the same email and try and submit it.

Given that it is a unique filename and email may have a checksum signature, it would be very beneficial for the system to warn that it has already been submitted. Much as Office does if an attachment has already been uploaded to the cloud.

Also check the other idea on ability to add file as a supporting document.