Migrating two separate AD instances to AAD

Question

Our company has just purchased another with their own AD instance. Both our AD instances are on premise. The company decided to rebrand and we've decided to accelerate our migration into Azure in the hopes it will make the merger easier. We need to create a new AD instance with a new company name within Azure, create a trust between the two on-prem instances, and start a gradual migration to the new AAD. Users would migrate in batches with their Exchange accounts but due to their size will take months to finally migrate everyone. How do I create a trust between the two on-prem domains and the AAD? Is there a better way to go about this?

Thanks

Answer 1

Using AD Connect to synchronize users from On-premise to Azure AD instance would be the first step. You can synchronize users from two different forests to a single instance of Azure AD. You just need to ensure the AD Connect server can talk to both the DC's

Check the following article for the prerequisites: https://learn.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-topologies#multiple-forests-single-azure-ad-tenant

Once you have the users from two orgs synchronizing to Azure AD, then you can manage them from a single instance and plan your mailbox migration accordingly.