жопа, this is a trickier question than that.
Linux always emails any output of the cronjob to the owner of the job. System crons email it to the root user (unless specified otherwise). User crontabs email the user. If you only care about the outputs, all you have to do is to set a working email address for that user. How you do that is up to the mail system you run.
However, to get notifications only when the cronjob is successful, you need to do more scripting than this, because you need to determine exactly what's considered successful and what's not. This varies from case to case.
Sysadmins typically integrate such scripts with their monitoring platform. I personally use Nagios and for example integrate my cron backup scripts with it so that I can monitor (and get notified) when the backups fail or succeed.
What gets tricky is what I meant by the case by case basis earlier. Even within the same use, like backup, there are servers I know will get errors when running a rsync backup on them because their files get modified very regularly and it doesn't matter so much if I have a few errors, so overall the backup is still a success. Whereas if I'm backing up database dumps and get a file error on any dump file, that's a failure.
If you can't be bothered scripting such things, just get the cron daemon to email you the whole output then you can manually shift through it and see for yourself.