for the display powersaving, I recomend going thru the display settings in the settings of wahtever desktop environment you use.
When the terminal tells that you have mail, its something the system itself has sent for you. I do not recomend turning it off, but instead, making all your safe cron jobs output their stuff into /dev/null. Anything they output during a run will be mailed to you.
If you want to tourn it off, take a look at 'biff' and the in.comsat line in /etc/inetd.conf