Start with the basics - can you email yourself from the CLI and receive the email ? Are you sending the emails to a DL or individual addresses ? Are the addresses all still correct or is there a comma or weird character in the config that might be blocking the send ?
Is the mailserver still configured in the CLISH ?
If everything looks configured correctly but you still don't receive any kind of email, maybe it's not your doing - can you still reach your mailserver from the Appliance or did something outside your control change ?
# curl -v telnet://mailserver.domain.com:25
Verify things one layer at a time: Network, OS, then worry about NetBackup. =)
