displaying, on a display screen, the single message document according to {HEAD ~ a conversational view} based upon {TAIL ~ a perspective} of the response level of a user within the mail thread 
based upon
displaying , on a display screen , the single message document according to { HEAD ~ a conversational view } based upon { TAIL ~ a perspective } of the response level of a user within the mail thread
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH