[Drakon]

Thanks for your comments! Works for me too!

I've changed the same:

$rcmail_config['imap_cache'] = 'db';
$rcmail_config['messages_cache'] = true;

and the performance has improved when opening folders with thousand of e-mails (with Roundcube 0.8.4 + Postfix + MySQL + Courier IMAP).

Thanks!