How many times can the prison send letters a month?

There is no legal limit on the number of letters sent. It doesn't matter how many times you send letters a month. However, if the contents of the letter hinder the investigation, prosecution and trial, the detention center may detain it and transfer it to the case-handling organ for handling. Whether the specific content can be passed or not is decided by the relevant competent department, but it is suggested that it is best to entrust a lawyer to contact the prisoner. According to the provisions of Article 28 of the Regulations of People's Republic of China (PRC) Detention Center:

During the period of custody, with the consent of the case-handling organ and the approval of the public security organ, criminals may communicate and meet with their close relatives.

Article 31:

Entrusted by the case-handling organ, the detention center can check the letters sent and received by criminals. Anyone who is found to obstruct investigation, prosecution or trial may be detained and transferred to the case-handling organ for handling.

In theory, detainees have the right to correspond and cannot write letters about cases. They can send them to prison and discipline, and there is no limit to how many times they write them.

In fact: not everyone can write, some prisons allow writing, and some prisons prohibit writing, depending on prison leaders and prison guards. If you have a good relationship with the prison guard, don't write letters, you can also make a phone call. There is no limit to the number of letters, but the process of writing letters is very long. Sometimes discipline is just throwing letters into the trash can. There is no minimum time limit. The key depends on whether there is a criminal act or not, and whether or not to bear criminal responsibility. If there is no criminal act or criminal responsibility should not be borne according to law, the person will be released naturally after investigation, and it may be within 3 days if it is quick. In judicial practice, detention is generally about 30 days. A criminal sentenced to fixed-term imprisonment of not more than one year, or a criminal whose remaining sentence is not more than one year, may also be supervised by a detention center. After the judgment takes effect, the prisoner will be transferred from the detention center to the prison where he served his sentence, usually within 15 days. Generally, prisoners in detention centers will be sent to prison within one month after being sentenced. If family members want to visit, the detention center will tell them when to send them away a few days before they are sent to prison. They can visit after they are sent away, and they can also visit after they are sentenced, but only relatives who are related by blood can visit.