how to update mail password using api - soap

I am using the mail_user_update.php
as an example to change passwords.
This updates the password but it does not encrypt it so we can't access the mailbox via roundcube or a mail client. I am thinking there needs to be an encrypt function?
can anyone help?

<?php

require 'soap_config.php';


$client = new SoapClient(null, array('location' => $soap_location,
'uri' => $soap_uri,
'trace' => 1,
'exceptions' => 1));


try {
if($session_id = $client->login($username, $password)) {
echo 'Logged successfull. Session ID:'.$session_id.'<br />';
}

//* Parameters
$mailuser_id = 794;
//$client_id = 15;


//* Get the email user record
$mail_user_record = $client->mail_user_get($session_id, $mailuser_id);

//* Change the status to inactive
print_r($mail_user_record);
$mail_user_record['password'] = crypt_password('gilbert');
print_r($mail_user_record);

$affected_rows = $client->mail_user_update($session_id, $client_id, $mailuser_id, $mail_user_record);

echo "Number of records that have been changed in the database: ".$affected_rows."<br>";

if($client->logout($session_id)) {
echo 'Logged out.<br />';
}


} catch (SoapFault $e) {
echo $client->__getLastResponse();
die('SOAP Error: '.$e->getMessage());
}

?>