Using an emailer plugin is the suggested way of solving this https://github.com/julianlam/nodebb-plugin-emailer-sendgrid
Getting upvoters and downvoters' names
Is there a way to display all upvoters and downvoters on a post, to all users that can see that post? It looks like that information is only available to an admin / mod by means of the modal, or the hover on the number (but only upvoters).
@Bri you will have to change core I think.