Why does Agari require all messages to be Journaled vs only External Messages?

Microsoft has confirmed that messages from an external sender spoofing an Accepted Domain internal recipient are not always journaled. For this reason, we ask that all messages are journaled to Agari, and the sensor will discard true internal to internal messages.    

Microsoft has stated the root cause is backend journal rule scope matching is simply a comparison of sender/recipient domains to the list of Accepted Domains to determine internal/external for sender/recipients.