Exchange 2010 to Exchange 2016 migration and URLs

Fellow experts, I would like your thoughts:
I have a very large 2010 to 2016 migration coming up and while normally I wouldn't have any issues but I see something I'm not 100% sure about.
They currently have 11 Exchange 2010 servers but we'll focus on 4 CAS servers. Two (2) are in each Active Directory Sites.
e.g.
ADSite1: 2 CAS servers with all URLs (including Autodiscover) is https://Smail.domain.com (Autodiscover Site scopes are configured)
ADSite2: 2 CAS servers with all URLs (including Autodiscover) is https://Nmail.domain.com (Autodiscover Site scopes are configured)
Currently have 2 dags (for mailbox servers in each site). i.e. no copies from one data center to the other.
they also do NOT have Outlook Anywhere Enabled yet (I know this will be required)

Customer is wanting unified name space (under my recommendation) to something like https://mail.domain.com and autodiscover to https://autodiscover.domain.com
I am also planning to do a single dag with copies of databases in each DataCenter.

So, I am planning 6 Exchange 2016 servers (3 in each location).

My question is around getting to unified name space without affecting clients before migrating.
Should I at least enable Outlook anywhere on all cas servers on 2010 and set url to https://mail.domain.com and change the autodiscover on the 2010s to https://autodiscover.domain.com before even installing the first 2016 server?

Or should I match all AD site URLs on the 3 2016 servers in each site to match the 2010 servers in each site then change the 2016 URLs post migration?

my thinking is I would change the autodiscover URLs on the 2010s, install the 2016s with all URLs to https://mail.domain.com and autodiscover to https://autodiscover.domain.com and enable outlook anywhere on 2010 and set that url to https://mail.domain.com (this would be one of the first things I would do even before installing a 2016 server).
Final note, They are getting a UC cert that will cover all of these names and their current cert already has autodiscover.domain.com.
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Alan CoxSr. Systems Engineer | Lead Microsoft CIE Qualified FacilitatorAsked:
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Jose Gabriel Ortega CastroCEO Faru Bonon IT - EE Solution ExpertCommented:
Hi Alan,
In my humble opinions, if you want to unify that you can just set the autodiscover.domain.com in 2010, while the scopes are set on the servers you should have no problem in the unification.

And then you can install the exchange 2016 servers and then set it to the exchange 2016 (always autodiscover service should be on the most recent version of exchange server, in this case, is 2016).

So the steps should be:

1. Match autodiscover services on both sites to autodiscover.domain.com (make sure that the site scopes are set on each one).
2. Test the autodiscover services,
3. Outlook anywhere on exchange 2010, isn't it enable it on each server?, I don't think it's enabled or a must for a migration
4. Deploy the exchange 2016 servers, and certificates, as well as entry, points SCP.
5. Setup coexistence, (setting up internal and external autodiscover and mailflow to new servers).
6. Move people
7. Remove Old items.

Good guidelines are set by the exchange deployment tool
https://docs.microsoft.com/en-us/exchange/exchange-deployment-assistant

About the certificate, they can get a Wildcard certificate and use it all around for their domains, new and old. and the cost will be cheaper than getting a certificate with 6 names (4 olds: 2 public nameservers and 2 autodiscover, and also the new unified autodiscover and mail)

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Tom CieslikIT EngineerCommented:
There is very useful Exchange Server Deployment Assistant in Microsoft site, that will walk you through whole procedure

https://technet.microsoft.com/en-us/exdeploy2013/Checklist?state=3229-W-AAAAAAAAQAAAAAEAAAAAAAAAAAAAwAMAAAA%7e

It is very good and it will show you all step by step moves.

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Jose Gabriel Ortega CastroCEO Faru Bonon IT - EE Solution ExpertCommented:
I had already referenced that one on my answer tom
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Tom CieslikIT EngineerCommented:
Ups.... Sorry
Jose Gabriel Ortega CastroCEO Faru Bonon IT - EE Solution ExpertCommented:
Haha np my friend :) lol
Alan CoxSr. Systems Engineer | Lead Microsoft CIE Qualified FacilitatorAuthor Commented:
Jose that is pretty much what I was thinking.  yes, Outlook anywhere must be enabled on the 2010s for sure. The deployment assistant isn't very helpful in this case. I've done 100s of migrations but it doesn't cover a situation like this but thanks Tom. I was just a little thrown by the changing of the URLs (I've done many after the fact) and the different autodiscover URLs.
Vidit BhardwajAdminCommented:
Changing the SCP for 2016 mbx server should not create problem if:

If you certificate with all the new namespace assigned to IIS.

If you have LB pointed to 2016 as this is capable to perform AutoD for 2010 mailbox.

In my opinion OA should be enabled as this will help users to connect outside network whose mailbox is on 2010.
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