When you migrate a user to Office 365 you want OWA users to have a simple redirect to office 365 and not get this error:
Also you want to give your users an easy OWA url not http://outlook.com/owa/mysupercooldomain.com
The solution is 2 steps
- create a cname record that points to outlook.com ( i.e. OWA.mysupercooldomain.com = outlook.com)
- add that record to your organization relationship
- set-orginaizationrelationship –targetOwaUrl http://owa.mysupercooldomain.com/owa
- Give OWA.mysupercooldomain.com to your users as there new owa page
Note: the domain you create the CNAME in must be one of your federated or accepted domains in office 365 for realm discovery to work.