Manually converting a Mail User to a Remote User Mailbox

The changes that need to be made are:

  1. Configure the user attribute targetaddress to contain the remote routing address for the mailbox. This should be in the format user@vanitydomain.mail.onmicrosoft.com. 
  2. Set the msExchRemoteRecipientType attribute for the user account to equal 4.
  3. Set the msExchRecipientDisplayType attribute for the user account to equal-2147483642. (yes, this is a negative value)
  4. Set the msExchRecipientTypeDetails attribute for the user account to equal to 2147483648