You should edit your crontab to send the various jobs output to /dev/null.
Code:
30 4 * * * /some/command > /dev/null 2>&1
The above entry will send everything (stdout and stderr) to /dev/null, so you will not be informed for errors
Code:
30 4 * * * /some/command 1 > /dev/null
The above will send only stdout to /dev/null, so will will be informed for errors.
Regards