How to stop multiple group emails from coming to your inbox?

To change your email delivery option, you must first sign in to the Google Account associated with the email address subscribed to the group, then please follow these steps:

1. Visit the Google Groups homepage
2. Click the "Manage my membership" link at the top (or possibly bottom) of the "My Groups" section.
3. Choose the email delivery option that you prefer for your group from the drop-down menu and save your change 

• Don’t send email updates
• Send daily summaries 
• Send combined updates (25 messages per email)
• Send me an email for every new message (about 3 per) 

http://support.google.com/groups/answer/46605?hl=en