Link to the Portal or Membership page?

When I email my members a new post, there is an upgrade link that takes them to the Membership page which shows the various plans.

When someone clicks on the plan, however, it takes them to a page where they can purchase with their credit card.

This is nice and all for those members who get my emails. But what if they forward the email to a friend, and then they want to upgrade? The flow is not clear how they will be treated since they haven’t actually created an account yet at this point.

Should the upgrade message in my emails link to the Portal instead? That would force them to login, or create a new account if they don’t have one yet, and where they could also change their upgrade plan.

How do most people handle this flow?

Thank you.

I would do the workflow yourself to a fully logged out you via email and check what you get, I assume you get the normal sign up dialog but its a few minutes for you to validate.