You can find request free Christian books by mail from a variety of churches and some non-denominational sites that focus on offering free samples. The books range from devotional-specific readings to how you might apply Christian concepts in your daily life.
Bibles for America offers free study Bibles and Christian books for daily living. To order books, click Order from the main page, and click Add To Cart to add the book sets to your cart. The books are shipped free of charge.
Market Street Fellowship also offers free Christian books as of 2015. There is a limit of one physical book per order, but it also offers electronic resources that can be downloaded free of charge if you want additional materials. Physical materials are sent via Media Mail and can take up to three weeks to arrive.
Sample Buddy has brought together a collection of sites offering free Christian books by mail. The books range from devotionals to recommendations on how to live a Christian life in today's society. When you find a book you want from the list, click it to link to the original website offering the book, and place the order through that website. Quantities are often limited, so if you find a book you like, you should order it immediately.