Cron sends mail after finishing job. How to turn off that?

[Kevac Marko <russian_knight degunino com>]

Hello.

I have a job which is started every 5 minutes. After every job user 
postfix receive a mail with subject: Cron <root rknight> 
/home/ffsearch/online_check.pl > /dev/null.
Mailbox is fullfiled with like messages.
What can i do?

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Fedora Core 2
Postfix
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P.S. Sorry for my English.