No reference this tiny can contain all the information you need. The sendmail source comes with many useful documents.
Describes all the changes that have occured from version to version.
Tells what is where in the source tree and gives a few cautionary general announcements.
Describes how to edit Makefile, and how to build and install sendmail.
Describes how to create a configuration file using the m4 technique.
Contains the Installation and Operations Guide. This directory contains the -me source and printer-ready PostScript.
Included with the source, is deprecated. Instead look for the most current FAQ that is periodically posted to the Usenet newsgroups comp.mail.sendmail and comp.answers. A link to the latest archived FAQ can be found at http://www.sendmail.org.
In addition to these documents supplied with the source, you can always find the most up-to-the-minute information at http://www.sendmail.org.