The real challenge is building out the back-end that deals with the service you select. (Unless you plan on handling unsubscribes manually, which might not be a

The real challenge is building out the back-end that deals with the service you select. (Unless you plan on handling unsubscribes manually, which might not be a bad idea if you are dealing with a low volume of users. IE: I'd pay someone $8/hr for an hour a day before I committed an $80/hr developer to spend a month building a system, until they are spending more than an hour a day dealing with orders.) I was consulting for a company where we spent weeks building and testing the back-end component that worked with Paypals API. Their API is embarassing. Instead of building a system that allows you to poll for unsubscribes daily, their server "pings" your server with data periodically. Imagine the difficulty of testing this out when they don't provide a way to simulate this. So if you do decide on a back-end, spend some time seeing if there is an open source component you can use to handle subscribe/unsubscribes. (Maybe ActiveMerchant?)