How can I configure the system to allow a company level user to use a single email address to access multiple companies without encountering an error?

How can I configure the system to allow a company level user to use a single email address to access multiple companies without encountering an error?

When a user tries to use one email address to create multiple company level profiles, the following error message will be shown on the User Profiles screen: Please select a different email address as email already exists.

A company level user can only be linked to multiple companies if they are within the same group of companies. If the companies are not grouped,  the user will have to create a company level profile with a different email address. 

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