Jpay makes it really easy to send emails to a prison inmate, all you have to pay for is the stamp price and you can pre-pay for the inmate to reply to you. You can go to jpay.com to check it out. They also have a phone app you can download.
Being locked up in prison, especially for long periods, can get pretty lonely. Receiving letters and gifts in the form of money or books, can really help make the time go by faster, and make the inmate feel like they are still cared about and connected to the world outside.