Please how postfix is used to send out SPAM?

Please kindly anyone help me discover where is the hole in postfix / system?

After i installed zPanel on plain linux OS CentOS, and some days passed i found /var/spool/postfix/deferred folder is growing

Here are two example emails headers:

http://pastebin.com/ZXnk4q42

Can please anyone tell from headers on how i need to fix the hole? I dont want to ban IP or such, but prevent anyone can abuse it..

Thank you

The first thing I would test for is an open relay. We can't test it for you because you provided no information identifying your domain, etc.

Thanks, no it is nto an open relay and open resolver test is also negative. i tried multiple online testers..

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