Active Directory Domain Consolidation

[prabks]

Currently I am involved in one of the AD consolidation project (AD Cross forest migration) and I have the current setup like this:

2 Domains abc.local and xyz.local in 2 different forest. I have single O365 tenant with 2 custom verified domains abc.com for abc.local and xyz.com for xyz.local) and I have 2 Azure AD connect 1 deployed in abc.local synching abc users and 2nd Azure AD connect in xyz.local synching xyz users (I know this is not Azure AD Connect supported topology but this is already been configured and its in the production). Now i have been assigned of consolidating AD as well as email domains. That is xyz.local will get merge with abc.local and xyz.com will get merge with abc.com. what would be the best way of achieving this consolidation without impacting email flow. 

[#2]

You didn't mention anything about your Exchange server configuration, but I guess you have one in abc.local and one in xyz.local. Is one of them already in hybrid mode or?

[#3]

No on-premise Exchange on any side, its only Exchange Online (O365)

[#4]

Ok, that makes it somewhat less difficult.. Would definitely go for one Azure AD Connect and move the users using migrate tooling.. As long as their source anchor doesn't change, the users should remain linked between AD en Azure AD

[#5]

What would be the best way to achieve this migration? if you can give me a high level steps that would be of great help .. I am planning to use ADMT for User/Computer migration. Current Source Anchor is ObjectGuid in both Azure AD Connect. Going forward I will have only one AD Connect.

[#6]

This is a nice article describing this: https://www.smikar.com/move-users-to-another-domain-and-retain-ad-connect-sync/

[#7]

I am planning to enable ConsistencyGuid feature from the existing AD Connect deployment as both Azure AD Connects running on new versions .. with this I will change source anchor from ObjectGuid to mS-DS-ConsistencyGuid and with the help of ADMT I will migrate a user along with mS-DS-ConsistencyGuid attribute and resync the User from the target domain. This should rejoin the objects from on-premises and the cloud. I will carry out this in my test and then do it in the production.