Sorry Jeff but you got this one wrong. None of this code belongs in your applications code. DKIM, rDNS, SFP, etc. should all be handled by your SMTP server, not your application. Your application is nothing more than an email client, like Outlook, Thunderbird, etc. Outlook isn't adding any DKIM info and individual users don't worry about DNS records, that is all taken care of by the SMTP server. And I would say SPF (what you call Sender ID) is just as if not more important than DKIM. It is not Microsoft centric at all, almost all mail systems and spam filters check SPF records. DKIM is almost exclusively used/enforced by Yahoo.