There are many places you can look for more information on sendmail. For a list, see the MAIL Howto posted regularly to comp.answers. It is also available for anonymous FTP on rtfm.mit.edu. However, the definitive place is in the sendmail+IDA sources. Look in the directory ida/cf below the source directory for the files DBM-GUIDE, OPTIONS, and Sendmail.mc.
Thu Mar 7 23:22:06 EST 1996