Email notifications are easy to setup.
You need to first check your server settings.
Please go through below link and ensure you have these settings.
Once you are sure about this. Refer below link to configure email in BPEL.
If you do these two steps correctly, notifications should work.
Thank you for valuable links.
I had some problem in server settings.
After going through the steps given in the link, I corrected mail server settings in EM console and restarted the server.
Now I am able to send email notifications.