To edit your email preferences click on your avatar in the top right corner of your screen and select Settings.
Next click on the Email preferences tab in the sidebar. From here you can adjust your email preferences. You can see the recommended settings on the screenshot below.
Email digest preferences
This option allows you to select between having discussion email updates per circle or having updates digested into one email for all your circles (recommended).
Email notifications for general activity
This option allows you to set the frequency with which you will get email updates. The default is once per day.
Email notifications for new circle messages
If your updates are grouped by circle, you will have the option to specify the frequency of updates for new circle messages. If your updates are grouped by digest, then your frequency will be controlled by the frequency of general activity updates above.