What is the legal responsibility for reading letters?

It depends.

First of all, who is the subject of peeking?

1. If it is an ordinary citizen, the voyeur can sue the voyeur for violating privacy; If the circumstances are serious, the voyeur will bear criminal responsibility for violating the freedom of communication and be sentenced to fixed-term imprisonment of not more than one year or criminal detention.

2. If the postal staff opens the mail without permission, it will violate the citizens' right to freedom of communication and bear criminal responsibility; He was charged with the crime of opening or hiding mails and telegrams without permission, and was sentenced to fixed-term imprisonment of not more than two years or criminal detention.