How to properly migrate users without changing the Atlassian account

[Malte Berg]

Hello there,

here is the scenario:

There are two companies (lets call them abc.com and efg.com) who are in a stage of merging;

• Both have an instance of Atlassian cloud. 
• Both are using MS EntraID for user provisioning and authentification.
• Both have set-up domains and claiming users.

Now one of the two companies will begin to migrate users from the EntraID tenant and Domain abc.com to the efg.com tenant and domain. 

At the same time the Atlassian accounts/instances should not be migrated at this time.

How can we make sure that the users will still have access to the abc.com Atlassian instance while having a efg.com account and e-mail address? 

I wanted to file a request with support but it seems like it only covers "proper" migrations which we don't need right now. 

Maybe someone can help me shed some light on this. 

Thanks in advance & cheers