Exchange 2010 coexist with exchange 2013

Question

Hi All ,
Planning to have a coexistence scenario in my environment which is mentioned below
Exchange 2010 - ambiguous url in place - OA enabled 
For mapi/rpc traffic - mail.domain.in -  exchange 2010
For https traffic - mail.domain.in - exchange 2010
mail.domain.in will get resolved in to cas array in exchange 2010 .
After coexistence On our side we are not going to move the mail.domain.in namespace to exchange 2013 , Instead of that we are going to use a new namespace in exchange 2013 for internal outlook anywhere and it will be outlookmail.domain.in and for the remaining
exchange 2013 services like pop,imap,owa,active sync url's,external OA will be having mail.domain.in as same as exchange 2010 namespace.
just consider outlookmail.domain.in is available on the san certificate installed in exchange 2013.
Note : 
On my ide I would assume Internal outlook 2010 mapi users will connect directly to exchange 2010 servers on the namespace mail.domain.in
Likewise i would assume Internal outlook anywhere 2013 users will connect directly to exchange 2013 servers on the namespace outlookmail.domain.in
Services like pop,imap,owa,active sync ,external OA connections for both exchange 2010 and exchange 2013 from the external world will be routed from firewall to exchange 2013 servers .Then https traffic for exchange 2010 mailbox users will be proxied to 2010
exchange server via exchange 2013 server.
question : I would like to know above mentioned scenario is possible or not ?
On my side I know in my environment i am having ambiguous url's in place and at the same time i don't want the exchange 2010 internal outlook users to connect via exchange 2013 rpc over http even though OA is enabled on exchange 2010.
So simply i can say i need my internal exchange 2010 mailbox users has to connect via tcp/ip.
All of you tell me your valuable suggestions.
Regards
S.Nithyanandham

Answer 1

Hi,
Going Straight to the point... and answering your question...
The scenario above IS possible For a while... But going ahead in the migration process, You'd face problems once the Exch2013 doesn't know how to handle MAPI connections:
As per Exchange Team...
In this scenario where both the MAPI/RPC and HTTP workloads are using the same FQDN you cannot successfully move the FQDN to CAS 2013 without
breaking your MAPI/RPC client connectivity entirely. I repeat, your MAPI/RPC clients will start failing to connect via MAPI/RPC once
their DNS cache expires after the shared FQDN is moved to CAS 2013.
As their recommendation, and I would tell you too by experience, the best option is to really use different internal and external URLs for the clients to connect to.
change your design to use a specific internal-only FQDN for MAPI/RPC clients. If you are in the middle of a 2010 deployment using an Ambiguous
URL I recommend you change your ClientAccessArray FQDN to a unique name and update the mailbox database RpcClientAccessServer values
on all Exchange 2010 mailbox databases accordingly. Fixing this item mid-migration to Exchange 2010 or even in your fully migrated environment will ensure any newly created or manually repaired Outlook profiles are protected, but it will not automatically
fix existing Outlook clients with the old value in the server field. 
So the overall for this first point is to enable the OA for all internal users, so as to ease the migration process in the future, even if for the time being its not necessary.
Also another point you should take into consideration is the version of yours OLK versions, as the minimum supported are as per below:
Outlook 2007: 12.0.6665.5000 (SP3 + the November 2012 Public Update or any later PU)
Outlook 2010: 14.0.6126.5000 (SP1 + the November 2012 Public Update or any later PU)
Outlook 2013: 15.0.4420.1017 (RTM or later)
I don't know the size of you network, but it might be necessary for you to use an inventory tool in order to identify that.
As advised, its really worthy to have a look at the following article, thus to clarify your view about this issue.
Ambiguous URLs and their effect on Exchange 2010 to Exchange 2013 Migrations
From <http://blogs.technet.com/b/exchange/archive/2013/07/17/3574451.aspx> 
Hope it can help you!
Cheers,
Think before you ask, give detail as much as possible, then ask and you will get help! Always have in mind, people do not guess! :)