Good news is you have found the right plugin to connect your website users through email group.
WPMG premium allows you to create stand-alone mailing groups like google groups or Yahoo groups. You don’t need pay monthly, per member or per mailing group. Pay once and start sending unlimited emails* to unlimited members* today. Some of the exciting WPMG features are:
-Unlimited mailing groups per domain name.
-Unlimited members per mailing group.
-Message moderation and archive functionality.
-Support and new feature requests.
See detailed features at: WPMG Pro Features.