Athena does not support the traditional ``mail'' command.  Please refer
  to the document "Electronic Mail on Athena".  This document is available
  in hardcopy for reference in each public cluster and for purchase at
  Graphic Arts Quick Copy Centers in the basements of Building 11 and W20.
  This document is also available on line: type "help" then select the
  topic "Communicating with Other Users" then "Electronic Mail".