I am going to try to be as concise as possible with this issue.
I have an Exchange 2013 organization that is in Domain A (A is the Forest Root). A new child domain was added recently, domain B.
DNS seems to be resolving correctly and /preparedomain:B.domain.com was ran to prepare the new child domain.
New mailboxes in domain B can log into OWA just fine, but Outlook does not auth (Login prompt appears repeatedly).
Using the Test Autodiscovery in the Outlook client, it seems to retrieve the server information fine, but if I go to the autodiscover URL and use one of my domain B user accounts, the login is rejected. A user account from domain A is accepted though.
Is there something with this new child domain that I am missing to allow Exchange to accept the login from the new child?