I would like to sell some digital goods on ebay but the problem now is for some of these sales paypal would probably ask for certain information (shipping details, invoice etc) and even if they don't ask right away, I would like to be cautious about this, So I would like to ask, would it be acceptable to send a confirmation letter via post to the buyer? At least that way I can get a tracking number to add on paypal or is there an online service that would provide me with tracking numbers?