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