You might send your shipping address to the vendor. Unless you have a PO box with a fake name, that's pretty personal, but even in the case of a PO box, you wouldn't want the feds to know where to intercept your package. Also, a sentence like this, "I sent the payment. Please ship the 100 grams of DMT to..." counts as a written confession. Read the Farmers Market indictment. Most of the evidence against them was taken from their Hushmail emails. If it had been PGP encrypted properly (on their computers, rather than with a key stored on Hushmail's servers), the feds would not have had 1/10th of the evidence that they used in the indictment.