Hi AM,
OK, sorry I was a bit tetchy there (trying to quit the evil weed). If you're using apache as your web server, look up its httpd.conf file and look for the ServerAdmin directive. You'll see something similar to:

# ServerAdmin: Your address, where problems with the server should be
# e-mailed.
ServerAdmin foo@bar.com
[download]

HTH

update: Though of course liz's response above is far more sane... :)