Our advice to keep your list growing: put a coupon or sale in every e-news you send. Reason: otherwise subscribers may unsubscribe. Also, subscribers are more likely to share your news.
If you want to consider this more: think about all the e-news you get from stores X Y Z. Why do we keep subscribing? Because we don’t want to miss a sale or coupon.
Take away, in the future always offer a percentage off or dollar amount coupon in e-news.