So I went to mail some knives today, and one of them is headed to Canada. On the customs form I put "collectible". They asked what it was specifically. I said a collectible pocket knife, and they were all WHOA NO WAY! YOU CANT MAIL THAT! 
Um, I do all the time. Plus, companies mail knives all the time. After some digging I found this on the USPS website
And more specifically
Okay it makes sense that they would be mad at a fixed blade in a paper envelope. Now, I fail to see any danger in a retail boxed folding pocket knife that is well packaged, but they would not accept it. Of course, I drove to the next post office to mail my "collectible figurine" without issue. When I asked about how companies send such things in the mail, they said the companies must "have a thing that lets them".
Has anyone else ever had a problem with this? I dont know that these are laws per say, but certainly appear to be the USPS rules.

Um, I do all the time. Plus, companies mail knives all the time. After some digging I found this on the USPS website
Restricted Matter
[7-28-14] Restricted matter is an article or substance prohibited or limited by title 18 of the U.S. Code. It also includes matter not otherwise restricted by 18 USC 1716(a) because it may, under conditions encountered in the mail, be injurious to life, health, or property. Examples of the type of restricted matter content moved to Publication 52, chapter 4, include:
a. Intoxicating liquors.
b. Firearms.
c. Knives and sharp instruments.
d. Liquids, powders and odor-producing materials.
e. Motor vehicle master keys and locksmithing devices.
f. Controlled substances and drugs.
g. Unsolicited promotional samples.
h. Instruments for use in animal fighting ventures.
i. Cigarettes and smokeless tobacco.
And more specifically
44 Knives and Sharp Instruments
441 Definitions
441.1 General
Sharp instruments include all sharppointed or sharpedged implements such as knives, tools, ice picks, razor blades, stilettos, or similar devices. When uncertain about the mailability of a sharp instrument or a switchblade knife, a ruling may be requested from the local postmaster (see 215.3).
441.2 Switchblade Knife
A switchblade knife has a blade that opens automatically by hand pressure applied to a button or other device in the handle, or by operation of inertia, gravity, or both.
Okay it makes sense that they would be mad at a fixed blade in a paper envelope. Now, I fail to see any danger in a retail boxed folding pocket knife that is well packaged, but they would not accept it. Of course, I drove to the next post office to mail my "collectible figurine" without issue. When I asked about how companies send such things in the mail, they said the companies must "have a thing that lets them".

Has anyone else ever had a problem with this? I dont know that these are laws per say, but certainly appear to be the USPS rules.