The following list provides additional sources for information about sendmail.
Home page for sendmail – http://www.sendmail.org
FAQ for sendmail – http://www.sendmail.org/faq
README for new sendmail configuration files – http://www.sendmail.org/m4/readme.html
Fatbrain.com for books about sendmail, particularly the second edition of sendmail from O'Reilly & Associates, Inc. – http://www1.fatbrain.com/catalogs/computing/subjects.asp?SubjectCode=OML