purging redundant segments from the mail thread by analyzing {HEAD ~ the thread identification field} to identify {TAIL ~ the redundant segments} 
to identify
purging redundant segments from the mail thread by analyzing { HEAD ~ the thread identification field } to identify { TAIL ~ the redundant segments }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL