Custom URL redirect to sharepoint online.

Hi all,

I am trying to create a publicly available redirect using my custom domain to sharepoint online "intranet.mydomain.com" to "mydomain.sharepoint.com"

I have create a CNAME in my external DNS to point to sharepoint but I get the following error.:

<h2>Our services aren't available right now</h2><p>We're working to restore all services as soon as possible. Please check back soon.</p>09+reZgAAAADI2oKRlEDuSpVHIaMJyiW8WlJIRURHRTE1MTQARWRnZQ==

Is there a simple way to create this redirect.