Lost Item

Hi, I have just received an email from a buyer to say he had not received an item I sent over 2 weeks ago. I sent the item standard parcels to the address listed on his paypal account and I have a proof of posting receipt. What do I have to do now as I feel bad that the item hasn't arrived and don't want to have to refund this as I will be out of pocket myself?

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Orignal From: Lost Item