The origin of nostalgic envelopes

Look at the mailing address. If you want to know where the nostalgic envelope comes from, you can check the mailing address and find out the source. Envelope is a bag-like device used by people to send letters and keep the contents of letters secret. Envelopes are generally made into rectangular paper bags, which appeared very early in China. (Qi Ce, the Warring States Policy) It was recorded that the emissary of the King of Qi asked Zhao in the factory, but the book was not delivered. Then he asked the emissary, "It's harmless at the age, the people have no ears" and "the book was not delivered", that is, the letter was not unsealed, that is to say, it was already there.