Sendmail is a very complicated program and its configuration is notoriously complex. You will find that you have sendmail on your Linux CDs, and if it is installed, its configuration file will be installed with it. It is probably safer to leave it alone if you don't understand it! You will find that it will handle mail delivery quite adequately unless you have a peculiar setup.
If you want to change your configuration but don't understand it, you could use linuxconf, which also handles other system administration tasks.
# Start the sendmail daemon: if [ -x /usr/sbin/sendmail ]; then echo "Starting sendmail daemon (/usr/sbin/sendmail -bd -q 15m)..." /usr/sbin/sendmail -bd -q 15m fiThis runs sendmail as a daemon (that is, it runs in the background, disconnected from any terminal session) and has it process its queue every 15 minutes.
Of course, if your system is not connected to your ISP, sendmail will not be able to send mail out; it will hold it in its queue and will keep trying to send it. You can check what mail is waiting to go out by the command
sendmail -bpIn order to get mail sent out, you have to make sure that sendmail processes its queue while your connection to the ISP is open. To do this, include the command
sendmail -qin your automatic mail script.