check /etc/cron.allow and /etc/cron.deny

check that the mail is not going to another mailbox (i.e the root of the prod machine), or that the mailbox of karl is not redirecting to another place, maybe out of the box. Try to put a CC order in the mail and see what happens

and take a look at crontab -u root -l and crontab -u karl -l in "prod", the line of cron can be in karl or in root and both can act differently. The crontabs for root and karl are in different archives also.