The book, arranged in 3 parts, provides postal historians and collectors of UK postal history with a comprehensive reference on the handling of undeliverable mail, the history of the Returned Letter Offices (RLOs), the stationery of the RLOs and the rules and procedures used in the RLOs.
- Part A handles the history of the RLOs based on extensive research in PO archives, including information on some of the PO officials who were influential.
- Part B lists the stationery of the RLOs including wrappers and envelopes used to enclose returned mail and forms and labels used. This is the first comprehensive listing since Dendy Marshall's listing of wrappers and envelopes in 1940.
- Part C presents a collection of documents, rules and procedures relating to the treatment of undeliverable mail, including complete transcripts of the rules as they were in 1897 and again in 1917.
The wide range of stationery used is listed. In 1912 most returned letter work was moved to Head Post Offices and several RLOs were closed. The book shows the effects of these changes.