When I once more did smo profile update for the successful backup, then I found in smo profile show o/p that Success operation of notification body got recipients e-mail address updated BUT THIS TIME Failure operation body configuration washed out. HOWEVER I started getting successful backup mail.
WHY I was not getting successful backup notification for the first time I updated my profile is because I run smo profile update for failure backup after I ran smo profile update for successful. Therefore it had deleted Successful operation configuration details in profile under notification body.
NOW WHY it is only saving either one notification configuration (Success/Failed) is yet to be find out. Not sure if I can declare it a bug or burt.
Anyway, here is in brief step as how I fixed the issue of not getting SMO backup success notification mails.
I updated smo profile update only for success. I didn't do for failed operation or else it will again wipe out success operation configurations.