Yes, you have access to their supporters' e-mail addresses. You can also use the "comments" section to make announcements, that will be sent to all your backers. Was your campaign mentioned in the media? Are there updates to the project? Do you need help from your backers to promote the campaign? This is the right tool to use.
We recommend that you use it to say thank you whenever you get a new contribution, keep your fans updated on news about the project and to arrange for the reward delivery. But do use it wisely: no one likes to receive spam!