補充一點

You should sent your material package as a "safe class", for example, "Certified Delibery" (the spelling or wors may not correct), thus, you can have a receiver from Post Office with a Post Office stamp. Keep this receipt well and if necessary, you can check tracking with is tracking number. And the Post Office can be a "ZHENG-REN" that the INS has received your material if some un-expected things take place.