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Scotch Tech
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Exchange 2013 - How does Outlook Anywhere connect Externally

We have 2 sites, Prod and DR. We're doing a DR test externally from an ISP perspective, no Exchange DB or server failovers. All mailboxes are in Prod (site1). External access goes to mail1.domain.com which goes to prod. We will be repointing that DNS to the DR site, which points to the DR exchange server. Prod and DR Exchange servers (site1 and site2) are in the same DAG.

When outlook anywhere connects to the DR Exchange server, it will say your mailbox is on Exchange server in the other site, what will happen? Does it use the External URL? Will it loop?

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Bradley Fox

8/22/2022 - Mon
Bradley Fox

You would want to set the external URL the same on both Prod and DR CAS servers.  When you have to failover you will need to change your DNS records to get users over to the DR site.  Change DNS for your OWA URL (likely something like owa.domain.com).  Set your autodiscover record as a CName and point at the OWA URL so all you have to change is the OWA (A) record.  Set the TTL on your OWA record to a low value, something like 300 seconds so the switch over is quick quick.
Scotch Tech

We only allow Outlook Anywhere, we block OWA. Is your instructions still valid then?
Bradley Fox

Yes, the instructions still work without OWA.  Either way you are just trying to get the clients pointed at the DR CAS instead of the Prod CAS.  Basically, you need to have the same configuration on both systems and will manually fail them over by changing DNS.

I'm not sure what the circuits look like between the CAS servers so when you fail DNS over you may need to manually force the database to activate on the DR CAS as well.  This would only be the case if the internet was down at Prod site but the servers were still able to talk to each other.  You do this using ECP, Servers on the left, Database tab, select your database and you can activate it on the other server in the right pane.
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Scotch Tech

But to confirm, we are not moving or failing over DB's they will remain on the Prod side, we just want Client access to come in via DR site, then internally Exchange to say " your mailbox is over in this site" and route over there.
Bradley Fox

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