Allow Roundcube to login with email adress

To allow Roundcube webmailer to login with email adress as alias for username configure config/main.inc.php as follows:

1. Add „virtuser_query“ to list of active plugins
// List of active plugins (in plugins/ directory)
$rcmail_config['plugins'] = array('virtuser_query', 'new_user_dialog', 'userinfo', 'markasjunk', 'archive', 'vcard_attachments');

2. Configure plugin to look up username by email address
$rcmail_config['virtuser_query'] = array(
'user' => 'SELECT u.username FROM identities i JOIN users u ON u.user_id = i.user_id WHERE i.email="%m"'
);

Login with email address then works after the user logged in once with username and created one or more identities.