It depends on the type of email you're wanting to send. There are two types:
Rewards Emails - these emails are sent whenever a reward is unlocked by a participant.
1.) First, you'll need to add a reward.
2.) At the bottom of your reward's details, there is a switch to "Send Email" switch that on and click "Edit Email":
3.) here you'll be able to edit the type of emails that your contestants will get when rewards are unlocked:
Confirmation Emails - these emails are sent whenever someone joins your contest.
1.) Go to your contest and then click on the "Settings" tab
2.) Scroll down and click on "Cheater and Security" and then click on "Edit Confirmation Email":
3.) Here you will be able to edit the Confirmation Email and how it looks whenever someone signs up to your contest. Make sure to click "Save Email" when you're done!