Team Chat - How to designate an external contact if they share the same email address domain

Can you make a user in the same organization an external user. We have contractors who have been given company email address but we want external user rules to apply when they are in a channel.

I am not sure if just adding via the add external contact path makes them an ‘external’ regardless of domain.

If it's possible, please describe how to do it. External contractor email: Jsmith *at mycompany. dot com 

Internal user email: Bdoe *at mycompany dot com 

UsingZoom cloud

* = @

Thanks,

Kevin