Returns TRUE if the
stream is still alive, FALSE
otherwise.
imap_ping() function pings the
stream to see it is still active. It may discover new mail;
this is the preferred method for a periodic "new mail check"
as well as a "keep alive" for servers which have inactivity
timeout. (As PHP scripts do not tend to run that long, i can
hardly imagine that this function will be usefull to
anyone.)