The packages from third party sellers (and are considered "publishers") have their return address label with the Amazon logo - it will definitely make it into the prison/jail. Do not spend the money on Fedex because that will certainly get rejected (unless it is legal mail).
https://www.inmateaid.com/ask-the-inmate/i-want-to-purchase-a-book-for-my-daughter-from-amazon-but-it-is-from-another-seller-not-directly-from-amazon-the-book-is-new-and-from-a-commercial-seller-but-it-will-send-from-jvc-books-not-amazon-1-will-the-book-be-rejected2-can-the-book-be-sent-fed-ex#answer
Accepted Answer Date Created: May 09,2013