I get it, but you're throwing technical specifications at a product/human/application problem.
No one wants to build an application that has to invent its own id scheme or manage this complexity. That fact that the specs don't provide a solution here -- something like informing you when an email address is no longer valid (again, I get it, this is hard/impossible) -- means that the spec will always be in conflict with actual usage.
No one wants to build an application that has to invent its own id scheme or manage this complexity. That fact that the specs don't provide a solution here -- something like informing you when an email address is no longer valid (again, I get it, this is hard/impossible) -- means that the spec will always be in conflict with actual usage.