I have ZCS 6.0.8 installed on Centos 64 bit.

I have decided to have my mails go through digital signature so I have installed opendkim and followed below link to set it up for my mail server.

Topdog.za.net :: Setup DKIM on Postfix with OpenDKIM

Everything went smooth but still I am not getting domainkeys worked. I have tried by sending an email to yahoo but in full header section it shows "dkim=neutral (no sig)"
"domainkeys=neutral (no sig)".

Also in the last of the above link for opendkim it is mentioned that "Append the OpenDKIM options to the existing milters if you have other milters already configured." What it means.

Please help me solve it.