Ok, you can set that up in a couple of ways, depending on your payment type:
1) if you have a shopping cart, you can add the publication as a product, and only have people added to the list after they've bought. Then, when you're broadcasting, you only send the messages to members of that list. (there's no online storage, though, so you'll have to create this yourself). Personally, I LOVE
1AutomationWiz (which is a 1shoppingcart product)
2) With PayPal, I'd suggest using a email broadcast service such as aweber (which is fantastic). Then, all you'd have to do is have PayPal send aweber an email (there's a simple process to get this going) and whoever pays for the publication will automatically be added to the broadcast list in aweber. THen, you can send your broadcasts directly to the list through aweber.
Above someone mentioned going with a very cheap service - this I
would not recommend. When you're sending out ezines - especially paid ezines - you need to ensure that your list is receiving your messages. 1AutomationWiz, Aweber, iContact, ConstantContact, and other respectable email broadcasting services charge $15+ monthly to ensure that your email messages are delivered on time to everyone in your list. They go through a painstaking process to make sure they're whitelisted, or allowed delivery. Free or very cheap publications don't offer the delivery rate and instead your emails will fall in a spam hole. And, if your email is caught in the spam hole in mass services (such a yahoo, gmail, etc.)
everyone using that service won't get email from your domain at all - sometimes even personal emails. The risk is too high, IMHO.
Best,
Erin