I’ve been working with the MailPoet plugin recently as a solution for emailing users of a site. One feature I sorely needed was a way to send emails to specific user roles, and alas this wasn’t possible.
I decided to make a plugin and it did the trick. I’ve consequently shared it on wordpress.org in the hopes that it helps someone out. This simply creates a list for each WP User role (custom roles included) and keeps the list synced when moving old and new users in and out of these roles.