======Synopsis:======
[[set]] notify_userhost_automatic [on|off|toggle]

======Description:======
If this is ON, several things occur. When [[on notify_signon]] is
hooked, a [[userhost command|userhost]](2) is issued on the person who
signed on. The $2 parameter of [[on notify_signon]] is set to the
person's user@host. When someone appears on the notify list whose
hostname is already in the internal list, it won't query the server.