1. users ("scorees") on your scorecard who have subscribed to receiving email notifications and whose emails are registered on their rise.global profiles (accounts).
2. followers of the scorecard - by default, a follower has to register their email against their rise.global profile (account)
You are only allowed to email when you have new scores/updates to share with your users & followers i.e. you are not allowed to use the email channel to send general messages.
The default email is shown below but you can customise the content of the email to a certain extent including adding images and content sections.
To access the email share channel, go to Share -> Email within your scorecard's adminstrator dashboard
The screenshot below shows you all the customisable options you have for the email format and content