There is more comfortability in not being on the same continent. Do you use a PO box? I would never use my home address. Too risky. Does it matter to you what they are in prison for when you choose who you'll write to? I know I'm sounding very prejudice but I'm only thinking of myself and the emotional trauma that could result from doing this due to my background. I just think you have to think of your own personal safety first. I'm glad that it gives you a sense of helping and I'm sure it means a lot to them too.