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