N. dubius seeds

More than three weeks ago I gave the dubius seeds within 19 letters to the post. I wrote to 2 of you which could get no seeds because they were out.  15 letters were sent to the USA , 2 to Great Britain, 2 to New Zealand and 1 to Australia. I fear that many letters didn’t arrive. It seems to me as if 8 letters to the USA and all letters to New Zealand and Australia are lost.
My questions now are: By which methods are the letters with seeds and small parcels with one bulb controlled? Will each letter and parcel be examined by  x-rays? Are there safe ways for sending?
Theo