You can see your notification preferences for a group by clicking "Control how often and when you want to receive emails from your notification preferences" at the bottom of your dashboard.
On your notification preferences page, you'll see four options: "All Emails," "Important Emails," "Daily Digest," and "No Emails."
All Emails will send you all the regular Pay By Group emails, including notifications when other people join your group.
Important Emails won't send you emails when someone joins the group or leaves a comment, but will let you know if the group's details change or if other major changes occur.
Daily Digest will send you one email a day with a summary of the day's events.
No Emails won't send you any emails aside from your purchase receipt after the transaction has completed.
You can get a digest in addition to other emails, if you want. To enable a daily digest, just click the slider at the bottom of your notification preferences page: