The sendmail book is considered by most to be the definitive book on sendmail. It is often called the ``bat book'' because of the flying fox (a species of fruit bat) depicted on the cover, as pictured above. The first edition was authored by Bryan Costales with Eric Allman and Neil Rickert and covered sendmail through version 8.6. The second edition was authored by Bryan Costales with Eric Allman and is the current edition covering sendmail versions 8.7 and 8.8. A list of errata for the second edition is available from http://www.sendmail.org/book_errata.html.
The sendmail Desktop Reference is a slim companion to the second edition for the sendmail book. It was authored by Bryan Costales and Eric Allman. A list of errata for the Desktop Reference is available from http://www.sendmail.org/desktop_errata.html.