This deadly racket uses letters to send Fentanyl and more dangerous drugs to dealers in the USA. Pure Fentanyl has a lethal dose in the average male of 2 milligrams. This is a small quantity. 1 gram will dissolve in 40 milliliters of water. The drug sellers then wet paper with the solution, it takes a few sheets. Then they dry it and laser print data sheets for anything and you will have 1 gram spread evenly through the paper, might be any data at all, the object is to make it pass inspection after it is mailed as innocent data sheets.
The USA buyer then washes the paper repeatedly with water - using repeated small amounts of distilled water. It might take 10-20 washes, one after the other, and it is then dissolved in the water. Then they have a solution they can evaporate to dryness, and they will recover almost 1 gram as a powder. With a laser printer very little black ink dissolves as particles, but if there are, it can be filtered before they dry it. If they use unsized and non glossy paper, and distilled water, the purity will remain and the final dry powder will remain potent. They then sell it. Since milligram doses are a nuisance, they often mix it with a powder - here is where the fatalities occur. It is very hard to make a uniform finely mixed powder. Drug companies have detailed procedures to mix fine powders with safety and uniformity, so they avoid any lumps. A lump can kill a person. Once they have their powder, perhaps they now have 1000 grams with a gram mixed in it - each gram of powder = 1/2 fatal dose. They then get a pill press and make 10,000 pills of 100 milligrams each = the same gram is now in pill form, with 1/20th of a fatal dose in each one. If the mix was well done and tightly pressed(the mixing powder will be chosen to make pills that are strongly bound as pills) they have an item they can sell, telling the buyer what is in each pill.
All is well - unless there were a few lumps in the initial separation = a few dead buyers/customers/addicts etc. There are some Fentanyl derivatives that are 15 times as toxic = smaller lumps can kill. The first class mail path is the safest, but most time consuming mail method. Expresspost is faster, but it is inspected more closely. There are other bulk methods, as listed on the DEA website here.
I am a retired chemist and the only way to deal with this on this side is rigorous inspection of the mails letter by letter with testers (which can be trained rats or other animals that can detect any drug odor - if at all possible).
China clearly does not have the will to rigorously deal with this problem, but they do have the power - if they are persuaded it is in their best interest?
https://www.dea.gov/galleries/drug-images/fentanyl
There is more data in that website, poke around to see the dimensions of this threat.