Yes, placing the line "/usr/sbin/sendmail -bd -q30m" in /etc/rc.d/rc.local will in fact make it execute at boot.
Now, to place it in there, use your favorite text editor like vi, pico, joe, etc.
Or.. you could just execute this: # echo "/usr/sbin/sendmail -bd -q30m" >> /etc/rc.d/rc.local
|