List all the authenticated domains associated with the given user.

**This endpoint allows you to retrieve all of the authenticated domains that have been assigned to a specific subuser.** This functionality allows subusers to send mail using their parent's domain. Authenticated domains can be associated with (i.e. assigned to) subusers from a parent account, and a subuser can have up to five associated domains. To associate an authenticated domain with a subuser, the parent account must first authenticate and validate the domain. The parent may then asso...