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