a thread level representing a response level of each of {HEAD ~ the at least two e mail messages} within {TAIL ~ the mail thread} and inserted into a thread level field; and 
within
a thread level representing a response level of each of { HEAD ~ the at least two e mail messages } within { TAIL ~ the mail thread } and inserted into a thread level field ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH