Did you configure the following section properly?
PHP Code:
// SQL Driver options
// ------------------
// PEAR database DSN for performing the query. By default
// Roundcube DB settings are used.
$rcmail_config['password_db_dsn'] = '';
// The SQL query used to change the password.
// The query can contain the following macros that will be expanded as follows:
// %p is replaced with the plaintext new password
// %c is replaced with the crypt version of the new password, MD5 if available
// otherwise DES.
// %D is replaced with the dovecotpw-crypted version of the new password
// %o is replaced with the password before the change
// %n is replaced with the hashed version of the new password
// %q is replaced with the hashed password before the change
// %h is replaced with the imap host (from the session info)
// %u is replaced with the username (from the session info)
// %l is replaced with the local part of the username
// (in case the username is an email address)
// %d is replaced with the domain part of the username
// (in case the username is an email address)
// Escaping of macros is handled by this module.
// Default: "SELECT update_passwd(%c, %u)"
$rcmail_config['password_query'] = 'SELECT update_passwd(%c, %u)';
The query should be something like:
UPDATE mailbox SET password=%c WHERE username=%u