While imap_status sets "read"-Flag when used, imap_num_msg does not touch any flag.
(PHP 4, PHP 5, PHP 7)
imap_num_msg — Gets the number of messages in the current mailbox
$imap_stream
) : intGets the number of messages in the current mailbox.
Return the number of messages in the current mailbox, as an integer, or FALSE on error.
While imap_status sets "read"-Flag when used, imap_num_msg does not touch any flag.