[imp] deleted messages preferences

[David JONCOURT]

Hi members,

I try to setup a config for basic users. They use Netscape for viewing 
their messages (in imap) in the Intranet and horde in other cases. They 
don't want to see their deleted messages. I thought I had the solution 
in the prefs.php file:
// hide deleted
// a value of 0 = no, 1 = yes
$_prefs['delhide'] = array(
     'value' => 1,
     'locked' => false,
     'shared' => false,
     'type' => 'implicit');

but when they connect after deleting a message with Netscape they still 
see the deleted message.

could you help me?

my config:
horde-3.0.6
imp-h3-4.0.4
imap

sorry for my poor english
thanks

David