Outlook client connectivity in exchange hybrid migration scenario (for mailboxes that have been migrated to O365, and on-prem mailboxes.

Hello Experts, I am planning on implementing a hybrid configuration for migration to O365. we have exchange 2013 on prem. My confusions are:

1. How will client outlooks connect to o365? i believe we are required delete our auto discover record in on-prem DNS (if one exists), and to create a cname auto discover record in on prem DNS, this will point the users outlook to O365, but how about users that have not been migrated to O365, how will their Outlook then connect to on-prem exchange, once this on-prem autodiscover is changed in on-prem DNS.

3. do i need to create this c-name autodiscover record in my public dns aswell?

2. what attributes of exchange online mailbox will i not be able to change if i decommossion my hybrid exchange servers after successful migration of all mailboxes (we have a couple thousand users, so this will be a few years in the future), but i would like to know the limitations of decomm of hybrid servers to limit on prem exchange foot print.

3.  the on-prem exchange server that we make our hybrid server, can it have User mailboxes on that server?

4. out internal AD is .net. however our user UPN is .com, and exchange organization name is also .com. what type of issues will we run into for directory synchronization?
do we need to change the user logon from domain\username to the users email address with UPN for all users for directory synchronization with Azure AD. the UPN suffix is already added for .com with the users UPN in our AD, but the users are currently logging on into internal environment as domain\username.

Please let me know.

Thank you
Newguy 123Asked:
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Jose Gabriel Ortega CastroCEOCommented:
1. Just set the autodiscover to the internal On-prem autodiscover, this will redirect to o365 all those users that are there.
2. In a hybrid you are not allowed to modify anything on the cloud, you will have to do it, on-prem, and it will be synced to the cloud by the ad sync.
3. No just set the autodiscover to the internal DNS (as I already said in 1).

2. Well decommissioning an exchange on-prem means that all your infrastructure will be managed by Azure AD or online identity, so you will be required to do the deploy of the computers into the new Azure AD. (like windows ten already have an option for this).

3.  yes it's hybrid you can have mailboxes on-prem and in the cloud.

4. None you will be synchronized the .com

5. Yes, you need to match emails to UPN for all users.

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Newguy 123Author Commented:
Hello Jose, thank you so much for answering. for the last question (question 5). once we select the user logon option to be via UPN, then they will have to log into their laptops using the UPN aswell, correct?, or am i mistaken...is it possible to have the users login to their laptops using domain\username, or do we HAVE to make them now login to their machines with their UPN aswell? i want to limit the amount of changes on the user side. Please let me know. Thanks
Jose Gabriel Ortega CastroCEOCommented:
nono ...
If you go to the AD users and computers.
Open any user
Go to the Account Tab.

You will see a couple of login options
Pre windows: domain\user

You can always use both, the thing is that you are used to working with the "pre-windows 2000", domain\user.
But they can log in with any of both, with their UPN or their domain\user.

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Newguy 123Author Commented:
i see. so if they can login with both, do we really need to change this on all users?, also one more question that just came to my mind, once a user mailbox is migrated to O365, does his/her outlook profile need to be recreated in his/her laptop? Thanks Joe
Jose Gabriel Ortega CastroCEOCommented:
Well, you can be as exquisite as you want.
but the best practice is that you need to have the UPN set for all the users in the domain. so you can skip that but it's not the best practices. I wouldn't do it.
Pete LongTechnical ConsultantCommented:
>> once we select the user logon option to be via UPN, then they will have to log into their laptops using the UPN as well

I wrote about this a while back it might help, (like you I had some concerns)

Changing Domain Users’ ‘User Logon Names’ and UPN’s

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