{HEAD ~ the external storage} is polled by the second application for {TAIL ~ the presence} of an encrypted electronic message, 
is polled for
{ HEAD ~ the external storage } is polled by the second application for { TAIL ~ the presence } of an encrypted electronic message ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH