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