Hi,
I think you need to change @ for + in
if (!empty($config['username_domain']) && !strpos($username, '@')) {
if (is_array($config['username_domain']) && isset($config['username_domain'][$host]))
$username .= '@'.$config['username_domain'][$host];
else if (is_string($config['username_domain']))
$username .= '@'.$config['username_domain'];
}
in program/include/rcmail.php.