I've been looking for a similar service in the past - found non. So I started it, mostly to build audience I was interested in serving. Almost one year later... with a very basic service mash-up of Carrd and Mailchimp we managed to grow with average 70 subscribers a month (with not much marketing and zero budget) and attracted some sponsors. We're growing this project beyond email to deliver crucial Amazon Seller news more effectively to people that need it!