[imp] Problem with Horde, IMP, Dovecot and Namespace

[absolutely_free at libero.it]

Hi,

I just migrated several mailboxes from a Postfix+Courier's server to another 
(Postfix+Dovecot).
Of course I'm using Horde (webmail edition 1.2.9) as webmail.
When users try to send a message, they receive this error:

Client tried to access nonexistent namespace. (Mailbox name should probably be 
prefixed with: INBOX.)

This is my 10-mail.conf in Dovecot:

namespace private {
  separator = .
  prefix = INBOX.
  inbox = yes
}




and this is my imp/config/servers.php:

$servers['imap'] = array(
    'name' => 'IMAP Server',
    'server' => 'xxx.yyy.zzzz',
    'hordeauth' => false,
    'protocol' => 'imap/notls',
    'port' => 143,
    'timeout' => array(IMAP_READTIMEOUT => 300, IMAP_WRITETIMEOUT => 300, 
IMAP_OPENTIMEOUT => 300, IMAP_CLOSETIMEOUT => 300),
    'login_tries' => 1,
);

I've tried this change:

$servers['imap'] = array(
    'name' => 'IMAP Server',
    'server' => 'xxxx.yyyy.zzz',
    'hordeauth' => false,
    'protocol' => 'imap/notls',
        'namespace' => array(
                'INBOX.' => array(
                        'name' => 'INBOX.',
                        'delimiter' => '.',
                ),
        ),
        'folders' => 'INBOX.',
    'port' => 143,
    'timeout' => array(IMAP_READTIMEOUT => 300, IMAP_WRITETIMEOUT => 300, 
IMAP_OPENTIMEOUT => 300, IMAP_CLOSETIMEOUT => 300),
    'login_tries' => 1,
);

..with no luck.
Any suggestion?

Thank you very much