I have read numerous articles on this topic and think I have the right plan in place to accomplish what I need done. I would like to roll it up and present it so this group can poke holes in it before I get myself in a spot I can't get out of. Thanks in advance.
Domain 1 = On prem AD - On Prem Exchange 2013 - Hybrid Configuration to O365 (Works like a champ)
Domain 2 = On prem AD - On prem Exchange - Connected with a 2 way trust to Domain 1 (not a sub-domain)
Our stated goals are (in order):
Migrate all user mail accounts in Domain 2 to Office 365, matching what exists in Domain 1 with minimal downtime and manual touch (trying to avoid .PST migrations)
Migrate all users from Domain 2 to Domain 1 with minimal downtime using ADMT
Collapse the old Domain 2 DC's in favor of Domain 1 DC's
Retire the on-prem mail server in Domain 2
How I think we can do this:
Create Domain 2 as a Trusted Domain in the O365 Tenant
Add Domain 2 as a Trusted Domain on the Domain 1 Hybrid Server
Migrate mailboxes from Domain 2 to O365 with batch migrations
Move user accounts from Domain 2 to Domain 1 using ADMT (to maintain the SID)
These are the reference links used to envision this plan:
Do I need a separate Hybrid Config in Domain 2 or can the Hybrid config in Domain 1 manage it all?
When I complete the Hybrid config does it update all public DNS records to route inbound mail to Domain 2 thru O365 - Thru the Domain 1 Hybrid - To the Domain 2 exchange server. (I know I am probably asking this wrong) - OR - Does mail still flow directly inbound to the Domain 2 exchange server until that mail account is migrated to O365?
When we start migrating user mail from Domain 2 to O365, it will be done with their Domain 2 user account in AAD. (user.domain2.com) will be added as an object in AAD. - OR - do those users need to be sync'd into AAD before I migrate the mailboxes. (probably asking this wrong as well)
Hope I have provided enough detail. I look forward to feedback.