You'd want some kind of "proof" it was mailed and/or recieved. Priority-mail legal-sized envelope (Flat-rate) $5.30 + delivery-confirmation is another $0.75. $6.05 altogether, and you get a confirmation back that it was delivered. (And even if it went awry, the post office would still have "proof" of the transaction, and I believe you keep a stub as well.) Mailed today, should get there by monday.
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