  Connectivity and topology are known to yield information about networks,
whose origin is self-organized, but the impact of {\it temporal dynamics} in a
network is still mostly unexplored. Using an information theoretic approach to
e-mail exchange, we show that an e-mail network allows for a separation of
static and dynamic structures within it. The static structures are related to
organizational units such as departments. The temporally linked structures turn
out to be more goal-oriented, functional units such as committees and user
groups.
