We have hybrid Configuration with Exchange Online with Exchange 2010 Servers, We have 30+ accepted domains in our environment configured\verified in On-premises Exchange & Exchange Online.
We have already move all our mailboxes to Exchange Online & also moved autodiscover of all our domains to Office365 but still we want to keep our Hybrid Configuration for Management & mail relay.
So we are trying to upgrade the hybrid configuration with Exchange 2016 Servers as Exchange 2010 is EOL.
When We ran hybrid configuration wizard, I came across the Hybrid Domains Page which is populating all our accepted domains & asking us to select the domains for Hybrid & select autodiscover for domain\s. I can see the domains which is part of the current hybrid configuration (Lets say only 7 domains, when we ran HCW in the past with Exchange 2010) are by-default selected. (I got these 7 domains from get-HybridConfigurations).
So my question is do we need to select all accepted domains on this Hybrid Domains page now which then will ask us to add TXT record in Public DNS for Domain Proof or we just need to go with the default selected domains (Lets say only 7 domains)?
what will happen if I won't select all accepted domains (only select 7 domains) in Hybrid Domains page & run HCW? will be there any impact on existing mailboxes in office 365 having email address of those accepted domains? As I said all our mailboxes are on office365, we are using Exchange on-premises for Management purpose (E.g. to modify mail related attributes & remotely creating mailboxes).
Also all autodiscover records now pointed to office365 so Do I need to select False for autodiscover for whatever domains I choose in Hybrid Domains Page?
Thank you in Advance.