General help

I would like to set up a course where enrollees are automatically subscribed to automatic emails from the news forum. However, I would also like to have a place on the website where people can sign up to recieve news by email via an automaed mailing list, regardless of whether they are enrolled in the course or not. My worry is that some people would join the course and also join the mailing list, and since I would intend to send the same announcements via both methods, some people would get double the announcements. Is there any way to avoid this?