Hi Yahoo is marking our mail as spam. We are using PHP Zend framework to send the mail. Mail header says that Domain Key is failed. Authentication-Results: mta160.mail.in.yahoo.com from=mydomain.com; domainkeys=fail (bad sig); from=mydomain.com; dkim=pass (ok) We configured our SMTP server (Same server used to send mail from zend framework.) in outlook and send the mail to yahoo. This time yahoo says domainkeys is pass. Authentication-Results: mta185.mail.in.yahoo.com from=speedgreet.com; domainkeys=pass (ok); from=speedgreet.com; dkim=pass (ok) Domainkey is added in mail header on our server which is used by both outlook client and PHP client. yahoo recognize the mail which is sent from outlook and yahoo does not recognize the mail from PHP client. As far as I know, Signing the email is done on the server side with help of domain key. PHP and Outlook uses the same server to sign the mail. But why yahoo handling differently? What I am missing here? Any Idea? Can anyone help me?