M365 Exchange server email flow problem

Question

[Scenario]
One country on-premises Exchange server is planning to migrate to M365 environment, the current setting would be:

1. The inbound and outbound email will go through headquarter exchange server and route to the country exchange server
2. Headquarter domain would be the email suffix
3. The country domain would be the smtp record
4. The headquarter would not be migrated to M365 currently

[Question]

1. How to change suffix record and not affect headquarter operation
2. How to set up the email flow for this case
3. If verify the headquarter domain in the country M365 environment and change MX record from headquarter DNS server will affect the operation

May I know any solution for that scenario many thanks

Answer 1

According to your information above, you have a Headquarter domain and country domain in your environment, and you want to migrate the users in country domain to o365 without migrating the Headquarter domain.

If so, you will deploy a hybrid environment, for the mailflow in hybrid, we could refer to the official document Transport routing in Exchange hybrid deployments

If your MX record points to EOP, you will need to enable the centralized mail transport, so the messages will all be routed to the on-premises Exchange server

If your MX record points to the on-premises organization, the message is delivered to an on-premises Exchange server

And the domain suffix changing in Exchange hybrid, refer to the steps in this link: add-a-new-domain-to-an-existing-hybrid-exchange-configuration

For more information about deploying Exchange hybrid Exchange Server hybrid deployments and Use the Microsoft 365 and Office 365 mail migration advisor