[horde] creating mailbox failed

[lst_hoe02 at kwsoft.de]

Hello,

we have IMP to handle authentication and point IMP to a Cyrus 2.4.17  
IMAP server. In the backends.local.php the IMAP admin user is set so  
Horde can list mailboxes and should be able to create mailboxes. The  
relevant setting is as follow:

$servers['advanced'] = array(
     'disabled' => false,
     'name' => 'MAILER',
     // imapproxy
     //'hostspec' => '127.0.0.1',
     //'port' => 1143,
     //'secure' => false,
     // Direkt auf Mailer
     'hostspec' => 'mailer.kwsoft.de',
     'port' => 143,
     'secure' => 'tls',
//    'hordeauth' => 'full',
     'protocol' => 'imap',
     'maildomain' => '',
     'smtp' => array(
     //    'auth' => true,
     //    'localhost' => 'localhost',
     //    'host' => 'smtp.example.com',
     //    'password' => null,
     //    'port' => 25,
     //    'username' => null
     ),
      'admin' => array(
          'user' => 'cyrus',
          'password' => 'some-password',
          'userhierarchy' => 'user.'
      ),
     'quota' => array(
         'driver' => 'imap',
         'params' => array(
             'hide_when_unlimited' => true,
             'unit' => 'MB'
         )
     ),
     'acl' => true,
     // Erst ab Cyrus 2.4 CONDSTORE und QRESYNC!!
     //'capability_ignore' => array('BINARY'),
     'cache' => true,
     'debug' => '/tmp/imap.log',
     'debug_raw' => true,
);

Unfortunately creating mailboxes does not work, it always return an  
IMAP error. This error is not included in the IMAP debug log, but with  
tcpdump i can see a "Invalid mailbox name" reply. This is regardless  
of the mailboxname i try.

Thanks for any help

Andreas