Problems signing mails with DKIM


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 and configured postfix for outbound as they explain but my mails aren’t being signed.
Testing in p.e. always returns
"The message does not have a domain key signature!
Domain-Key Status: NOT PASSED

Please help me… :frowning: