sendmail config files

primary config file is /etc/mail/sendmail.cf
cryptic syntax, but straight text
much like /etc/passwd, not directly modified
/etc/mail/sendmail.mc : rules for creating sendmail.cf
m4 is a macro processor/language
/etc/mail/sendmail.mc is at least semi-readable
instead of putting: Djlinux-classes.com directly in /etc/mail/sendmail.cf
we put: define(`confDOMAIN_NAME',`linux-classes.com')dnl into /etc/mail/sendmail.mc
the rules followed by m4 for building the file are in: /usr/share/sendmail-cf
Why use m4? portability to upgrades!
Tips: comment out the DAEMON_OPTIONS line (why?) remove postfix (why?) install sendmail-cf (why?) set domain name (why?)