DKIM Documentation for Rackspace Mail Customers without Cloud Office?

[duaneking]

https://github.com/rackerlabs/support-how-to/blob/master/content/how-to/rackspace-email/enable-dkim-in-the-cloud-office-control-panel/index.md does not contain instructions for adding DKIM if Cloud Office is not used due to the noted concerns.

How would one go about adding DKIM without that?

After all if Rackspace really is in support of security, then they should offer that, right?