To authorize Rackspace Cloud Office to send emails on your behalf you will have to include it in your SPF record. The SPF record mechanism used for Rackspace is shown below.

include:emailsrvr.com

Rackspace support DKIM signing for your custom domain. For more information and instructions on how to enable DKIM for your domain please click on the button below.

Create a free OnDMARC account to test your configuration.