Client Access server "%1" couldn't find a Client Access server of version %2 to redirect traffic for mailbox "%3". Outlook ...

Client Access server "%1" couldn't find a Client Access server of version %2 to redirect traffic for mailbox "%3". Outlook Web App requires every Internet-facing Active Directory site to contain at least one Client Access server that's running the previous version of Exchange and at least one Client Access server that's running the current version of Exchange. Make sure you have at least one Client Access server of version %2 exposed on the Internet.