Oh not this shit again. I thought the Chinese stopped playing that game a year ago.
Basically after packs were brought in by one of the Chinese logistics companies, another company would slap labels printed with recycled USPS tracking numbers, which fooled the "good enough for government work" USPS systems into thinking they were valid postage paid. Went on for years and years while they didn't bother to stop it, hundreds of millions of dollars stolen from USPS, and then cried to congress for bailout money and raised postage on the rest of us.
This finally ended with thousands of packs from China stopped with that "counterfeit postage" tracking message.
That's why I can send a package faster, more reliably, that'll arrive in better shape, 30% cheaper with UPS (who's drivers make over $100k) or FedEx than USPS.
USPS loses US$150m in counterfeit postage scam - read more about this with Parcel and Postal Technology International
www.parcelandpostaltechnologyinternational.com
The other problem is it gives USPS the right to open the pack. Unlike customs, US Postal Inspectors don't send "love letters". They have a history of pursuing enforcement, so it exposes customers to serious risk,