DKIM setup on CentOS / Courier MailServer

Our VPS box is Linux CentOS with CPanel. There's a courier MailServer installed (by default). It seems we've successfully implemented SPF & DomainKeys. But we also need DKIM, since we're having some problems with our mail being delivered into Spam folders of Yahoo Mail (all the time), and Gmail / Hotmail (sometimes). We're looking for a someone to successfully implement DKIM on our server, in a way that DKIM check will be a "pass" (currently neutral) by [login to view URL] and Yahoo. This can be checked by sending mails from the server to Yahoo Mail & Espcoalition test account. Yahoo would show if DKIM is successful on the detailed mail headers. Espcoalition would return the results with an email. Once this is done, the job will be complete. However, we sometimes need general server administration skills. Also, even DKIM may not solve our problems with Yahoo. So we may, in the future, need someone with a good record of mail server administration (high deliverability to major service providers). So this basic assignment, which should be an easy job for sb. who has the know-how, is a good way to start an ongoing relationship. Once the job is accepted, we want to see successful implementation within 24 hours (because it should be a very easy task for the experienced). Thanks for your interest.