PHP. Руководство по PHP. 2005
imap_ping
imap_ping
Description
bool imap_ping (resource imap_stream)Returns TRUE if the stream is still alive, FALSE otherwise.
imap_ping() pings the stream to see if it's 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.
imap_open
imap_qprint
Отвечу на любые вопросы. С уважением, Дмитрий Владимирович.