Preparing your Office 365 subscription
As you prepare for integration with Office 365, one of the first and most important steps is to ensure you have registered all your User Principal Names (UPNs) and e-mail domains you plan to use with the service. This also includes any e-mail domains you plan to coexist with but will leave on-premises. Let's recap on why both UPNs and e-mail domains are important to register.
A UPN is an individual's log on to Active Directory. In many cases, you are likely to use domain\%username% as the user log on. We need to change this to their UPN, which is also likely %username%@domain (in some cases it may be domain.local or a public domain.com). We need to ensure your UPN is a public domain. Ideally, we should have the public domain match the user's primary e-mail address.
E-mail domains are also important to register within Office 365. First off, you cannot assign a primary or secondary e-mail address to a mailbox if the e-mail domain is not registered with...
