Having the cron daemon send email alerts could be a useful feature, but it could also get very tiresome depending on your setup. To disable this feature do the following.
Edit /etc/crontab with your favorite text editor, modify or insert the following line
Should you have crontabs set up for different users, use
and insert/edit the relevant configuration parameter as seen above.
Or should you want to disable output for certain jobs you could add
0 1 5 10 * /path/script.sh &> /dev/null