When a cron job generates output on either stdout or stderr, the output gets mailed to the owner of the crontab. Now, you can specify an alternative email address by setting the MAILTO environment variable in the crontab, but this applies to all jobs in the crontab.
So, if you want the output of different jobs to get mailed to different users, then you can just redirect the stdout and stderr of each job to the mail command like this:
13 02 * * * /bin/backup 2>&1 | /usr/bin/mail -s "Cron <root@exobox> /bin/backup" \ user@example.net