You can now control the email notifications for each group you are in.

On the group page, at the bottom of the list of members, you’ll now see a link to “Edit your group settings”. Click that to set your email options for discussion posts (like this) and comments on the mapping. You can also leave the group by clicking the link in there.

It’s recommended to keep emails for the discussion posts at least, so you can be notified of developments in the group.