if you are running netbackup for windows, first you have to install and configure blat http://www.blat.net/
All you have to do is explained in the following technotes:
If you find it complex, and it is, you can use opscenter to create alerts and reports much easily.
You have selected Linux as OS.
NBU does not have a built-in mail client.
Before you configure anything in NBU, you need to ensure that sendmail (mailx) can be used as root user to send emails.
Once this is working, you can use Global Properties to send email for failed backups or else Universal Settings to send email for all backups.
DOCUMENTATION: Email Notifications Settings and Their Behaviors