Ability for idea portal users to subscribe to notifications for new ideas Merged

Some of our idea portal users have requested they get notified of new ideas submitted, so they can vote on any that are relevant to them. As I doubt all users would want this, we'd like to see the ability for idea portal users to have the choice to subscribe to new ideas, so only they receive this. 

As a solution, maybe they receive a daily/weekly summary of new ideas, rather than an email for every single ideas, to avoid getting too many notifications.