Domain Keys fail (bad sig) problem

We are using PHP Zend framework to send the mail. When we sent mail to yahoo, Yahoo headers says that Domain Keys fails (bad sig). We have set up the DKIM, DomainKeys in our server. We configured our server in outlook and sent the mail to yahoo via outlook, at this time yahoo headers says that domainkeys=pass (ok);.

Why yahoo treats the mails differently even though same server is used to sent the mail via outlook client and PHP Zend program?

We have captured the network packets when the mail was being sent from both client(outlook and Zend). After comparing both headers, we found out that Outlook has communicated the server with IMF开发者_如何学Python(Internet message format) protocol, From, to, subject,date,Mime boundary and ext all are sent via this IMF protocol. But out PHP's Zend framework does not use this IMF protocol at all.

Is this IMF protocol important for yahoo to understand the mail authenticity? Or not using IMF protocol is not a problem?

What is misleading the yahoo to say our domainkey signature is bad?

Gmail is accept out domain key signature.

I hope some experts can help me to sort out this problem. Thank you?

By

Ravi