What is the significance of using imap_expunge() function in conjunction with imap_open() in PHP?

When using the imap_open() function in PHP to access an IMAP mailbox, it is important to use the imap_expunge() function to permanently delete any messages marked for deletion. This ensures that the mailbox is properly updated and that the deleted messages are removed from the server.

$mailbox = '{imap.example.com:993/imap/ssl}INBOX';
$username = 'username';
$password = 'password';

$inbox = imap_open($mailbox, $username, $password);

// Process mailbox here

// Delete messages marked for deletion
imap_expunge($inbox);

imap_close($inbox);