If you cronjob exit with a non-zero value it typically sends the error message as an email to root. But since you have been getting those emails you probably want to capture the error messages to a file. You can do this my redirecting standard error to a file. Do that that add the string  /tmp/error.txt 2>&1 to your cronjob entry. It would look something like this:

1 * * * * /usr/whatever/foo > /tmp/error.txt 2>&1
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