A manager can control the default email frequency and amount of emails that go out to the group members. 

Each member can update their own preferences (here) later under their own account settings. If a member changes their own email preferences, they override the default group settings for themselves only.  

Group Email Frequency options

A manager can control the default frequency for emails sent for a given group. In the group's settings (gear icon on the left nav bar > Email Settings), a manager can toggle the following on or off:

• a digest of the new posts from each day -- If enabled, this will send a daily digest of new posts from the group to members by default.
• every new post as it is created -- if enabled, this will send email notifications for all new posts as they are created by default.
• every new comment as it is created -- if enabled, this will send email notifications for all new comments as they are created on all posts by default.