Hotspot Question
You have an Exchange Server 2010 organization. You plan to upgrade to Exchange Server 2016.
You have two active directory sites configured as shown in the following table:
You have five servers configured as shown in the following table:
You have three users who have mailboxes configured as shown in the following table:
Answer: 
Can anybody confirm: Yes, No, Yes?
This kind of looks like a trick question. I have a feeling it’s:
No, No, Yes.
User1: Brussels is not internet-facing. Even if an OWA externalURL is set, it doesn’t matter. I think User1 will be redirected to CAS02.
Please provide a positive comment and insight if I’m incorrect.
Yes, No, No
After a user has authenticated to an internet facing CAS server, the CAS server attempts to locate the location and version of the users mailbox.
– If the user is local, the mailbox is rendered.
– If the user is NOT local, then use the AD Routing information supplied by the “Microsoft Exchange Active Directory Topology” service to locate a CAS server in the site hosting the user’s mailbox. If an external URL is configured on the CAS server in the second site, then silently redirect to the URL available or redirect the user to the link supplied. If the external URL is NOT specified, and an internal URL exists, & the authentication method on the virtual directory is set to windows integrated, then proxy the request.
https://social.technet.microsoft.com/Forums/ie/en-US/5d15809c-7e31-4482-a547-56a9d636c5a5/exchange-2016-redirection-of-client-access-requests?forum=Exch2016MFSM