When creating a business contact, the system will validate the email address and not allow you to create an account if the email isn't unique.When importing companies you can choose to not create duplicate companies if the name and postcode already exists.
There should be validation when creating a new company via the UI that will flag if the company name and/ or the postcode is not unique. The user should be able to create the company anyway, however having the company being flag will let the user know that the company already exists.
