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?