It's a loss and as it's been said before don't reply to the letter. If you have a reputable source, send him the letter and he should resend the gear free of charge.
I don't know about flagging the PO boxes..that may be true. But I know for a fact that customs does not flag names or residential addresses with regards to gear..other stuff maybe, but not AS. Take it from someone who knows what he's talking about. No disrespect to members here on this forum but most here know very little about the logistics of how customs works.