There should be no need to migrate anything, just update any relevant properties for the users. For those users that have email addresses associated with domain B, you might consider keeping the original alias as a secondary one, at least for a time, in order to avoid any mail delivery issues (as external recipients will have no way of knowing the address has changed).
Migrate Users from Domain to Domain in same tenant.
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Hello.
We have 2 domain "A" & "B" in same tenant ( Business basics) .
Domain A is on premise domain with Exchange on cloud and Domain B users are On cloud only.
We need to move Domain B users to Domain A but keeping them only Cloud only and deleting domain B.
Do we need to migrate mail boxes or just change their UPN and SMTP address?