Before you can do anything with the mbox file, you need to create an instance of the Mail_Mbox class and open() it.
<?php
require_once 'Mail/Mbox.php';
$mbox = new Mail_Mbox('/path/to/mbox');
$mbox->open();
//do more here
?>
After opening the file, you can retrieve single messages via get(). The size() method helps you to determine the number of messages:
<?php
//... initialisation
for ($n = 0; $n < $mbox->size(); $n++) {
$message = $mbox->get($n);
//do something with the message text
}
?>
If you're done working with the file, close() it.
<?php
//... other code
$mbox->close();
?>
Also have a look at the Mail_Mbox examples directory in
/path/to/pear/docs/Mail_Mbox/examples/.