Identify email user which generating traffic

Hi all, Anyone can help me ? Today is second day when I have crazy traffic through POP3 I found in forum this command: grep *****co.com /var/log/maillog* | grep retr= | grep -v retr=0 | awk {'print $11'} | cut -d, -f1 | cut -d / -f2 | awk '{t += $1} END { print "total: ", t, " bytes transferred over POP3"}' so this is a result: total: 574669361274 bytes transferred over POP3 So my question, how I can found user (email) which generate this traffic ?! Thanks