{HEAD ~ a thread level} representing {TAIL ~ a response level} of each of the at least two e mail messages within the mail thread and inserted into a thread level field; and 
representing
{ HEAD ~ a thread level } representing { TAIL ~ a response level } of each of the at least two e mail messages within the mail thread and inserted into a thread level field ; and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH