cron - send mail

[VIROKILL]

is it possible to use cron to send an email to someone or a list of people every 30 mns or and hour or day ect.

[webwise]

Yes. Please take a look here (http://expressionengine.com/downloads/details/cron_send_email/)
You will need ExpressionEngine Cron plugin

[mgolvach]

You can also just set this up in your crontab - assuming every 30 minutes, just add this line to your crontab

0,30 * * * * (echo "Subject: Cron Email";echo;echo "This is your email. Enjoy!")|/usr/lib/sendmail bob@bob.com,joe@bob.com,jim@bob.com

Pretty much just make sure you pass all the arguments you'll be piping to sendmail in a subshell (by using the parantheses), otherwise only the last echo will get sent through the pipe as sendmail's STDIN. You can make this is as complicated or simple as you want.
Of course, if it's going to be more complicated, it would be easier and less cryptic to write a quick shell script to send the email and then call that from cron

Best of luck :)

, Mike