When you use the Follow Project widget in your consultation, it allows participants, registered or unregistered, to 'follow' any of the published projects and effectively become a subscriber for project updates. You may read the article on Encourage participants to follow your projects for the details on adding the Follow Project widget in your project.
The list of subscribers to this widget is collated and made available to you in the newsletter, where you can decide to send the newsletters to the subscribers of a project. Choose the checkbox option Include project followers when selecting the recipients of the newsletter to ensure that your project followers receive the email.
To determine the full list of project followers, click the View button next to recipients.
This displays the the full list of recipients with screen name and email. You can unselect any recipients you do not want to include in the communication.
Read the article on Sending Newsletters to your database for the detailed steps on sending an email newsletter.