Hybrid migration provides integration between an on-premises Exchange organization and Microsoft 365 Exchange Online. It can be used in two scenarios: as a method of migration between an on-premises Exchange Server and Microsoft 365 (Exchange Online) or as a permanent state for your on-premises Exchange and Microsoft 365 organizations.
A hybrid deployment offers companies the ability to extend the functionality of an existing on-premises Microsoft Exchange to Exchange Online. This provides a single space between an on-premises Exchange organization and Exchange Online in Microsoft 365.
The following topology example provides an overview of a typical Exchange 2016 deployment. With a single-forest, single-domain organization with two domain controllers and one Exchange 2016 server installed, we start deploying and configure a required Azure AD Connect server and use the Azure AD Connect password synchronization feature to let users log in with the same credentials for both their on-premises network account and their Microsoft 365 account. Then we complete the hybrid deployment prerequisites and use the Hybrid Configuration wizard to select options for the hybrid deployment.
Your new topology will have the following configuration:
Users can log in to the on-premises and Exchange Online organizations with the same username and password (“single sign-on”).
User mailboxes located on-premises and in the Exchange Online organizations will use the same email address domain.
All outbound mail is delivered to the Internet by the on-premises organization. The on-premises organization controls all messaging transport and serves as a relay for the Exchange Online organization (“centralized mail transport”).
On-premises and Exchange Online organization users can share calendar free/busy information. Organization relationships configured between on-premises and Exchange Online also enable cross-premises message tracking, MailTips, and message search.
The same URL is used for the connection to mailboxes for both on-premises and Exchange Online users.