Use this for final solution , login your admin ,click on Servers------>localhost----->File Manager---->home---->Kloxo------>httpd---->webmail----->roundcube----->config------>config.inc.php
Edit the config.inc.php with the following details and save.
$config['smtp_user'] = ''; edit to this $config['smtp_user'] = '%u';
$config['smtp_pass'] = ''; edit to this $config['smtp_pass'] = '%p';
save and you are good to go......