I don't think you can do it from the moble app, however, you can do it on the website:
1. Click on "Your Profile"
2. Click "Edit"
3. On the left had side, towards the bottom, click on "List Subscriptions:
4. To the right of each thread, check the box for any threads that you don't want email notification.
5. At the bottom of each page, there is a drop down menu, select that and pick the option that you want..