imap php

Am trying to connect to my fedora 14 64bit imap server using php the code is below.

However, I am getting the following error and don't know where to start to solve it
"Can't open mailbox localhost:143INBOX: no such mailbox "
Any Ideas?

<?php
$host = 'localhost:143';
$user = 'user';
$password = 'password';
$mailbox = "{$host}INBOX";

$mbox = imap_open($mailbox , $user , $password);
$str = imap_errors();  echo("imap_errors():\n");  print_r($str);

if (imap_ping($mbox)){ print "success";}
else                 { print "fail"; }

imap_close($mbox);

?>

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