Any takes on why the following code works on one server and not the other.

<?
// Mail account
$mailbox = "{www.xyz.com:110/pop3/notls}INBOX";
$mailacct = "user@xyz.com";
$mailpwd = "xxxxxxxxx";

$mbox = imap_open($mailbox,$mailacct,$mailpwd) or DIE(imap_last_error());
?>

Server on which the above works has the following config:-
PHP - 4.2.3 - Imap 2001 with SSL and with Kerberos

Server on which the above fails has the following config:-
PHP - 4.3.9 - Imap 2004a with SSL and with Kerberos

Error Message received :
Warning: imap_open(): Couldn't open stream {www.xyz.com:110/pop3/notls}INBOX

The domain xyz.com is on a remote server separate to the 2 servers that we tested on.

Any takes would be appreciated.