Email reuse from deactivated accounts

Does anyone know of any standards or generally accepted rules for giving out someones old email address to a new customer.

The reason I ask is: A family member recently (3 months ago) closed their account with their ISP and lost access to their email. Ok fine. But if I send email to that address I find that they have already given it to another customer. I think this is a big security issue and could leave the family member open to identity theft.