Most prisons permit prisoners to accept mail, although the items which can be mailed to prisoners are usually heavily restricted. In order to send mail to a prisoner, you will need his or her address at the prison, and you may find it useful to contact the prison to find out which items are permitted in prison mail, as restrictions vary. If you are just sending a letter, it can be mailed in a conventional envelope, but if you are sending additional material such as stationary, stamps, photographs, or writing supplies, enclose it in a manila envelope and clearly label it for mail room staff. Be aware that all incoming prison mail is opened and inspected, and that staff will confiscate prohibited items.

The requirements for addressing prison mail vary, depending on where the mail is being sent. In general, the first line of the address should include the prisoner's full name, along with an inmate identification number. Next, the prison name and specific housing block of the prisoner should be listed, along with the city, state or province, and postal code. You should never enclose cash, sensitive items, or other valuables in prison mail, as they will be confiscated.

If you are sending supplies to a prison, make sure that they are allowed in prison mail. You may need to call the prison to find out about supply guidelines. Typically, most prisons allow prisoners to receive writing paper, pens, stamps, photographs, greeting cards, and news articles or Internet clippings. If you are mailing material from the Internet to a prisoner, you should cut and paste the material into a document, as some prisons will confiscate material with a web address. In addition, prison mail cannot contain obscene or violent material. If you want to send books, most prisons require the bookstore to mail them directly.

To send money to a prisoner, you should use a prison-approved wire transfer company. Most prisons take a percentage of funds sent to prisons to supplement the state victim's compensation fund, and the prison will provide more information about that. In general, the amount of money which an inmate can receive is also restricted, so be sure to ask the prison about the maximum amount that you can send to a prisoner. You can also send checks or money orders in prison mail, but they may take longer to clear, as the staff will have to process them.

Some organizations offer relationships with prison pen pals, so that prisoners with few friends on the outside can still have an opportunity to get mail. Numerous websites connect people interested in pen pals with potential correspondents, and many pen pal organizations process all of their pen pal mail through a central clearing house, meaning that the prisoner will not have your address unless you choose to give it out. The guidelines for mail sent to pen pals are the same as those for regular prison mail.