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How would you go about implementing DKIM signing in this scenario?

  • You have a service that allows customers to logon to your web application, create a newsletter, and send it to their subscribers using their domain name. (Like MailChimp, Constant Contact, etc.)

  • Each customer will have a different domain name.

  • The mail will be sent through your servers.

Is there a way for the customers emails to be DKIM signed without adding a DNS record for their domain? Is there a way to have the emails coming from the providers domain but have the customers "from" address?

Zach
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You could use the Sender: header for this - put your domain in the Sender: header and sign with your DKIM key. The From: header would continue to specify your customer's domain. This approach is condoned by the DKIM specification (RFC 4871, appendix B.1.4).

You should be aware that many mail clients will display the Sender: header in addition to the From: header (gmail says "On behalf of"). Also I'm not sure whether in practice your deliverability with this approach will be as good as it would be if you signed with a key in the From: domain. I suspect that using the From: domain's key will always give the best results, but that would require sticking a key in your customers' DNS.

Community
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AGWA
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  • AGWA i agree with you and we are on the same page as Zach's problem. We use INterspire as platform for sending email on behalf of our client. The application creates user account and inputs their company email as from email and its not using our domain as authorized sender. We would like to configure our mailer to do the same use our authorized sending domain on behalf of client just bu changing the Envelope header to be our domain as permited sender. Did you find resolution to your issue. Please share –  Sep 03 '13 at 23:05