After fighting a bit with Mac os X to get the ssh tunnel working, I learned that on many BSD systems, you have to add the line:
groups = yes
to the smtp xinetd config file for it to work. You might want to add that info to your page. Except for some of the paths being different, it just works. Here it is:
service smtp { disable = no socket_type = stream protocol = tcp wait = no user = root server = /usr/bin/ssh server_args = -q -T -i /var/root/.ssh/smtpkey u@gw.net groups = yes bind = 127.0.0.1 }
I think the official way to make xinetd read the config files is to send it the HUP signal, e.g.
'killall -HUP xinetd'