The red and express satchels only have tracking to the nearest delivery centre so you will not have any proof that it was sent to the buyer's address, if you want Paypal protection you have as a minimum to provide proof of posting to the buyer's postcode so even if it shows as delivered to the mail centre it will not do any good with Paypal unless the buyer happens to live in the same postcode area. If you don't bother getting any receipt at all surely you don't expect Paypal to just take your word for it that you posted anything to anybody. In future if you want Paypal seller protection send with signature required or click & send.