If you’re selling anything via Paypal, you must collect your buyer’s emails into a unique buyer’s list. This buyer’s list, if treated right, can continue to bring in revenue far into the future. I’m still receiving several thousands per month from a buyer’s list I created in 2009. However, you do not need expensive, 3rd party software such as DLGuard or Nanacast to automatically add buyers to the 3 major autoresponders on the market.