Since I installed, every now and then a random group I am subscribed to turns to "beta" status. This means the group now appears in a "groups beta" section of the app, and you receive an e-mail notifications for every single comment in the group. For large groups this could easily render your inbox unusable. The app doesnt allow to toggle mail notifications, nor does it allow to unsubscribe from groups. All notifications via email do contain an unsubscribe link. However, the link leads to a full blown website which isnt usable on a phone.