Customer want to create a user in their account but system says it is already in use in another account.
Administrators have a functionality called “Mark User Obsolete”. This action is applicable only on deactivated users.
This will internally rename a user firstname.lastname@example.org to email@example.com.<orgid>.obsolete ;
It allows you to use firstname.lastname@example.org in another tenant. An obsolete user can again be activated only be removing activate tag.