Installing an Edge Role Server as a domain member server works with Exchange 2013 CU10

And maybe CU9. Haven’t tested that, but nonetheless, it didn’t work before CU9. So why install into an existing forest instead of the recommended DMZ or Workgroup?  Edge Roles can do more then just “Edge” stuff. They make great open relay servers within your org, let you leverage Powershell and beat the pants off any IIS/SMTP stack you may be running. By installing into an existing forest as a domain member, you can use your domain creds of course, which is a good thing. If you have the licenses, go for  it. The Edge role is right in the Exchange admin’s wheelhouse.

Consider the Edge if you need an open SMTP relay in your org. Options are good.