Chain link fence, by Engin_Akyurt at Pixabay
Many Christian Ministries are concerned about prisoners. One of the best-known is Voice of the Martyrs which maintains a prisoner alert page. Voice of the Martyrs has features that allow concerned people to write letters to prisoners and officials.
Although not explicitly a Christian ministry, another site that allows individuals to contact prisoners (in the United States) is jpay. It charges a few cents for a “stamp” to send your email, but is well worth the price. You can look up the prisoner you are trying to contact if you have basic information and if the prisoner has become a member of jpay. You can also send money to prisoner accounts through this system where institutions allow it.
For Links to individual Prison Ministries, visit the International Directory of Prison Ministries