imap_expunge()

(PHP 4, PHP 5, PHP 7)

Delete all messages marked for deletion

说明

imap_expunge(resource $imap_stream): bool

Deletes all the messages marked for deletion by imap_delete(),imap_mail_move(), or imap_setflag_full().

参数

$imap_stream

由imap_open()返回的 IMAP 流。

返回值

Returns TRUE.

@eisbrenner at gidn dot de
You shouldn't call imap_expunge until before closing the connection. imap_delete tags a message for deletion, imap_expunge deletes all tagged messages. i.e.:
for ($i = 0; $i < $num; $i++) {
 imap_delete($box, $i);
}
imap_expunge($box);
imap_expunge should not be in your inner loop.

imap_expunge() may change order of messages which were loaded using imap_sort(). 
That means, if you use foreach() on result of imap_sort() function and each pass you move/delete a message and instantly expunge them, next cycle, messages will have different numbers than imap_sort() returned and the script will fail.