Exactly what does Paypal require for proof of postage?

I send everything at large letter rate, as my items are so small, so I don't use Click & Send or anything fancy. Larger orders I send registered post, and the PO gives me a register receipt with the registered number sticker on it.

 

If something doesn't arrive, do I actually have any proof that satisfies Paypal that I've sent the item? I used to think registered post was all I needed, but the receipt and number don't actually have anything on them that shows the recipient's address.

 

Up until recently, I used to be given a "lodgement receipt" to fill out, but the PO never gives me any paperwork anymore. Should I be asking for it? Would a stamped lodgement receipt satisfy a Paypal claim?