Migrate and Link few of users from Rackspace email server to Microsoft Exchange of Office 365

Hi,

We have purchased Microsoft 365 subscriptions for a few of our users. We are currently using the email exchange of Rackspace.

We have configured Office 365 with the same domain as Rackspace (i.e. a specific user at Office 365 and email address at Rackspace email server are the same "mailto:user@abc.com)

Is it possible to migrate a few users from Rackspace email server to Office 365 (Microsoft Exchange), whereas all other users remain at the Rackspace email server ?

Thanks