In order to add SPF and DKIM keys to the domain, you need to use the Client Area.

To begin with, create the keys themselves:

After you have the keys:

  1. Go to the Client Area;
  2. Click Domains > DNS Management;
  3. Click Records edit at the domain you want to attach the keys to;
  4. Create the new TXT record with the keys you need;
  5. Click Add.