Help – how would you set this up?

I am in the early stages of building a blog as an addition to a static website.

My question is more on the theoretical side than the actual how-to – but I will need that as well to implement I’m sure.

Currently -> we have an email list that is private (only paid subscribers). This list can generate up to 1500 messages a month. We have a constant problem with emails bouncing, getting marked as spam, etc.

I want to -> migrate all of this into WP, and helping the subscribers set up news readers to handle the majority of the current emails.

Because this is a fee-for-service, how do I set it up so the general public can’t get access without paying?