Source : Free On-Line Dictionary of Computing

sendmail.cf
     
         {sendmail}'s configuration file, which it reads
        once when starting up, usually found in the /etc directory.
     
        Only real {Unix Gurus} can understand, let alone modify, this
        file since it consists moslty of {header} {rewrite rules}
        written as {M4} {macros}, as well as various other one- or
        two-character commands.
     
        (1996-12-09)