How are Outlook Anywhere clients Proxied from Client Access Server to Mailbox (in same site)?

K B
K B used Ask the Experts™
on
Where is the official Microsoft documentation on this?

I have read: https://technet.microsoft.com/en-us/library/bb310763(v=exchg.141).aspx

but this seems to only cover OWA, ActiveSync, IMAP & POP.  It does mention that clients (probably Outlook) use the CAS server (role) to obtain availability and autodiscover information... BUT ... is that all?

Thank you.
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Top Expert 2015

Commented:
RPC over HTTP is used by OWA and Outlook Anywhere.
K B

Author

Commented:
Would you agree that OWA encapsulates at the server and Outlook Anywhere is sending RPC calls encapsulated by HTTP directly from the client.
I am speaking of the client traffic to the server.
K B

Author

Commented:
oh wait this question is asking about how Outlook (making a request of a CAS server) is proxied to its Mailbox.  More specifically, when the CAS server lives in a subnet that is the SAME as the mailbox server.

Is it CAS to CAS proxying or a direct connection from CAS to MBX server?  Any supporting documentation?
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Top Expert 2015

Commented:
Entourage 2008 web services edition was first to use this protocol - i.e browsing OWA site under the hood.
K B

Author

Commented:
that's cool but any thoughts on my last post/the question?
Top Expert 2015
Commented:
hi K B,

To be specififc, OA uses RPC\HTTP. The RPC endpoint is the CAS box which "Proxies" your connection to your mailbox, also on RPC\HTTP.

So, from your Outlook client, there is an RPC\HTTP connection to the CAS box on port 80 (non SSL) or 443 (SSL), then there is a connection from the CAS box to the Mailbox Server using the same RPC\HTTP protocol but on port 6001.
In simple terms the CAS role acts like a gate way to forward the traffic to the server where the mailbox is located. If the mailbox moves servers (failover, migration etc), your rpc connection to the CAS remains and it re-establishes its RPC connection to the new Mailbox Server. Which prevents Client (Outlook) disconnections.

How your client finds the CAS server is another tale... but to correct you, it doesn't use the CAS to find Autodiscover, it's the other way around.
The Autodiscover DNS and SRV records or SCP provide a URL where the CAS box can be located.

Regards

Guy

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