Getting A REAL Pen Pal

How to get a "pen" pal - a writing buddy from within prison walls. Why would you want to? Is anyone not allowed to have mail? How is the mail censored? What is not allowed in? What is not allowed out? Is there a limit to the mail - the number of letters that can be sent or received? Are there any taboos or rules for letter writing? What’s a DC number and can you get a letter to someone in jail if you don’t know the correct address? How can you get the correct address? Are there pen pal programs available and who sponsors them? Are there any rules? What about the fear of wondering what might happen when your pen pal gets out?