Can I mail seeds in the U.S. Mail?
If so, will they be x-rayed and rendered sterile?
I have a friend I’d like to swap seeds with on some fairly hard to find plants (flax, hyssop, calendula, comfrey), but I want to be sure they won’t be damaged.
FaerieBeth
You can’t mail seeds to Uzbekistan.
That pretty much sums up everything I could find about seeds at www.usps.com
If the Postal Service were in the habit of destroying seeds, the mail-order seed companies would be out of business pretty quick.
Gee, now all my SCA friends in Uzbekistan will have to go without Fern leaf Dill and Calendula 
The reason that I asked was I seemed to remember something about x-rays and seed destroying scanning of the mail going on after the whole anthrax episode. I didn’t know what postal protocol was, and I wasn’t sure if the seed companies may put something special on their packages to designate no x-rays or what have you.
FB
I think that they’re still just sterilizing mail headed to the federal government. The process is expensive and time consuming, so it makes sense to just protect high value targets.
Here’s a list of things which would likely be affected by the dose used to sterilize mail. Seeds are not listed, but this is probably an oversight, as 40 to 50 kGy will mess with a seeds DNA.
As far as the legality of mailing seeds goes, it depends on what you are mailing and where. Different states have have all sorts of odd laws regarding importation of agricultural material. If you want to be totally aboveboard about your mailing. check out the relevant states department of Agriculture (or similar) websites.
I did a bit more digging on mailing seeds, and came up with a few old (~2002) sites that talked about the possibility of the post office irradiating all mail, but nothing since then. If irradiation were a problem today, the seed companies and heirloom tomato growers would be very concerned about it. They’re not, so your seeds will probably be OK.