Problems signing mails with DKIM

Hi,

I can’t sign my mail with DKIM. I tried everything and I still can’t get it… I need your help!
I’m using it with postfix+procmail.
I followed the instructions on this page http://home.messiah.edu/~jlong/dkimproxy/ and configured postfix for outbound as they explain but my mails aren’t being signed.
Testing in http://www.mailradar.com/domainkeys/ p.e. always returns
"The message does not have a domain key signature!
Domain-Key Status: NOT PASSED
"

Please help me… :frowning: