First, see this post to see how you can send an email from terminal. Once you solved this problem and you can send emails from terminal, the following method should work to setup cron job to send emails.
Edit the crontab entries using
crontab -e command (by default this will edit the current logged-in users crontab) and add the following line:
0 0 * * 1,3,5 $HOME/scripts/send_email.sh >> $HOME/tmp/out 2>&1
Now you should create
send_email.sh script. Something like this:
recipients="email@example.com firstname.lastname@example.org email@example.com"
cat $HOME/email_message | mail -s $subject $recipients
$HOME/email_message is the message (file) you want to send.
Don't forget to grant execute access for the script:
chmod +x $HOME/scripts/send_email.sh