‎Co-existence of both Exchange server and Online without having a Hybrid Server

[Curious_Kevin16]

Hi Techies,

I have a scenario where an Exchange Server 2013 based mailboxes (a global setup) should be migrated to Exchange Online. This should happen in a staged manner however, we do not want to use Hybrid setup (a 3rd party tool will be used for mailbox content migration)

The requirements are:

1. Exchange environment is a global setup of multiple servers. This subjected organization is a one sub entity of the mother company (DAG is being used) so this migration would be a cross-forest one.

2. We'd like to migrate a few mailboxes well in advance (may be 5 from a one department) and test the mail flow in the 365 environment before proceeding with the rest of the mailboxes. This would be there for few days for interim period. How do we keep the domain name working across both environments (i.e. inbound outbound mails on migrated 5 accounts should be directed to 365 while the rest of the mailboxes will remain intact in on-premises)?

3. How do we keep the domain name/MX/DNS record working on both environments to segregate the migrated and non-migrated mailboxes to function in their respective location? is it possible to achieve this without having a Hybrid server?

Note: Exchange Servers will be completely removed after cut-over once everyone migrated to 365 and tested.

Appreciate your thoughts and Ideas !!

[#2]

Note: i think you should reconsider your strategy.

On the side:

If you move 5 mailboxes in advance, then the only way is to set a forward on the source onpremises mailbox to a new mail address where the mailbox moved to in the target tenant. Remember outbound email will having this mail adres for those 5 users.

Email kan be delivered only once. There is no way where to check the mailbox is located for other mailservers as you really asking.

I think a big bang is better or to use a hybrid coexistence ... with the relationship and mail flow rules on both exo and on premises...