My mailserver is sending spam

Hi,

I have problems with my mailserver since it is sending out spam. I cant find anything in my loggfiles that indicates that my Kerio is sending spam. I have everything setup nice, with dkim and all other stuff i need. The header in the mail i am getting back from hotmail, doesnt indicate that it is sent with dkim.

How can my server send those spam, and where should I start to look?

joakim