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CasparABO-8058 avatar image
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CasparABO-8058 asked GustavoRodrigo commented

Pre Cutover Exchange 2010 to Exchange 2016 migration

Hi, our client has one Exchange 2010 Standard server. We have successfully installed Exchange 2016 standard in the domain and now we are preparing to do a cutover of DNS records from 2010 to 2016. After that we will migrate mailboxes and eventually decommission the old 2010 server.

I have a question and I think it has to do with the fact that we did not perform the cutover yet. Everything and everyone is right now still connecting to the 2010 server at this point. All DNS records point to 2010 (internally and externally) We will be using the same name webmail.company.com with certificate etc. All Virtual Directorys have also been named the right way.

It seems that Exchange 2016 can proxy stuff back towards Exchange 2010 (webmail for example) also there is mailflow between the 2 servers with a test mailbox.

If user A (2010 mailbox) logs on to EX2016\OWA he ends up in 2010 OWA, all good.
if user B (2016 mailbox) logs on to EX2016\OWA he ends up in 2016 OWA, all good.
if user B (2016 mailbox) logs on to EX2010\OWA he gets an IIS error

I believe this has to do with the fact that Exchange 2010 cannot forward everything towards 2016, but 2016 can do it towards 2010 ( After cutover )
Also at this moment we can setup an iPad and (externally) connect to user A (2010 mailbox) If we want to setup user B (2016 mailbox) account cannot be verified. I believe this also has to do with the fact that we have not done a cutover. Exchange 2010 cannot forward this credential / mailbox lookup to 2016?

Is this normal behavior? I would like to know before moving on to the next step. It makes sense to me that this is happening but I will have to plan the cutover with the 100+ users...

office-exchange-server-administration
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EricYin-MSFT avatar image
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EricYin-MSFT answered GustavoRodrigo commented

Yes, that's expected behaviour.
Proxy functionality is only down-level. This means that client accessing Exchange 2016 can be proxied to Exchange 2010, but clients accessing Exchange 2010 cannot be proxied to Exchange 2016. You can see an example in second part of this blog: Client Connectivity in an Exchange 2016 Coexistence Environment with Exchange 2010
You also need to update SCP url, which is used to help domain-joined machines to connect to Exchange server in Outlook:

 Set-ClientAccessService -Identity EXCH2k16 -AutodiscoverServiceInternalURI   “https://autodiscover.domain.com/Autodiscover/Autodiscover.xml”

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I have just installed a virtual machine in the network and used it's host file to point to the new server. Everything works exactly as planned. Also the issues above are solved it seems. going to webmail.company.com ends up at the 2016 OWA page. Logging in with users that still have their mailbox hosted on Exchange 2010 get redirected back to Exchange 2010 OWA. Sending email internally and externally all works. Outlook test profiles all still work without any certificate or username/password prompt.

Thanks for the information and confirming this was the actual issue. always good to understand what is happening.

We will now plan the actual DNS change and email flow change and it should be good to go


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Hi @EricYin-MSFT,

Can i install Exchange 2016 in another AD site (Example: Site B) without migrate any user mailbox and while Exchange 2010 SP3 still reside in a main AD Site (Site A - internet facing) without changing or afecting mail flow or pointing the DNS records to an AD Site B ?

When we are now ready to migrate the mailboxes, this need to be done before or in pararell while mailbox is moved from Site A (Exch.2010) to Site B (Exch.2016) ?

Thanks.



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CasparABO-8058 avatar image
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CasparABO-8058 answered GustavoRodrigo commented

So to sum up the questions. When all mailboxes are still on the 2010 server, do I have to point all DNS records and mailflow to 2016 first before it is even possible to really use co-existence? Can Exchange 2010 up-proxy towards Exchange 2016? Or can Exchange 2016 only proxy back to Exchange 2010?
I would assume that by moving mailboxes from 2010 to 2016 while DNS still points to 2010 will cause issues for the mailboxes that have been moved off to 2016.

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Same question here! What to do first?

Can i install Exchange 2016 in another AD site (Example: Site B) without migrate any user mailbox and while Exchange 2010 SP3 still reside in a main AD Site (Site A - internet facing) without changing mail flow or pointing the DNS records to an AD Site B?

This need to be done before or in pararell while mailbox is moved from Site A (Exch.2010) to Site B (Exch.2016) ?

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