How to find the person who wrote the anonymous letter?

Anyone who finds an anonymous letter can apply for criminal police intervention in various ways. Xin Jinghui uses a series of technical means to detect the profiter, including his paper notes and mailing address. As long as he posted a stamp, he must have a mailing address if he can remember it. If it is a printed version, you can also analyze where this person is by the model of the printer.