During the registration process and on the personal account page, the visitor can indicate whether they want to be kept informed of upcoming events. If you create audiences in Stager, make sure you include these opt-ins in the process.
Under Marketing - Contacts - Audiences, for example, you search for everyone who is interested in 'Poetry'. Before you send a marketing email to this entire target group, include in a new rule that you only want to find contacts who have checked an opt-in. These will only be the contacts who have indicated that they want to be kept informed.