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