shipping plants through the mail

[kiki-do]

I was wondering if anyone else has ever had a problem shipping orchids through the mail. I went to ship a package the other day using USPS, and was told I couldn't ship plants. I had to convince the postman that orchids are not in soil, etc. I feared I would have to open the package and show him, (took me awhile just to get everything situated in the first place) but he eventually let it go....very reluctantly.
What are the rules about sending plants through the mail within the USA. I could see if the package was being sent to another country, but not the case here.
Even greenhouses send regular houseplants to customers through the mail, right?
Next time, I won't put "fragile, live orchids" on the box.
I didn't know! I only want them to be handled with care. Pointers anyone?