  Email graphs have been used to illustrate general properties of social
networks of communication and collaboration. However, increasingly, the
majority of email traffic reflects opportunistic, rather than symbiotic social
relations. Here we use e-mail data drawn from a large university to construct
directed graphs of email exchange that quantify the differences between social
and antisocial behaviors in networks of communication. We show that while
structural characteristics typical of other social networks are shared to a
large extent by the legitimate component they are not characteristic of
antisocial traffic. Interestingly, opportunistic patterns of behavior do create
nontrivial graphs with certain general characteristics that we identify. To
complement the graph analysis, which suffers from incomplete knowledge of users
external to the domain, we study temporal patterns of communication to show
that the dynamical properties of email traffic can, in principle, distinguish
different types of social relations.
