If you're on aol, there is a list in the free area.
The house server can be reached via househlp.house.gov
Senate server wasn't listed but try www.senate.gov, gopher.senate.gov,
There seem to be no "rules" ;-) regarding e-mail addresses but there seem to
be some conventions.
Senators often use their title and @last name
ie senator @sonso.senate.gov Some use first and last name
ie highest firstname.lastname@example.org
Reps are a bit more idosyncratic best to look them up but try