Ossn sends a email if someone register on your website. If someone didn't receive the email there are few things that need to be checked:
Please contact your hosting provider to ensure if you have php send mail enabled or disabled.
Php send emails are disabled by default on following hosting companies:
If mail server is enabled and you still having difficulties in getting emails, make sure your hosting ip is not blacklisted. If your ip is not blacklisted please check if you have something in Ossn error_log file.
If your emails reaches into spam folder ask your hosting provider to provide you trusted ip, and ask them to add a reverse dns records for your domain.