To stop recieving the e-mails from the boards, you have to sign in, Click here. and select "Read on the web" This setting will only forward the weekly update and any manager announcements. You also have the option of a daily digest, a summation of the groups activities and posts each day. If you use "inbox", You will recieve an e-mail every time somebody posts something on the board. Managers can not change it for you. Once you select Read on the web for the entire group you can also go back to individual threads that you do wish to recieve and set just them to send you mail if you want mail from them.
Another source of unwanted e-mail is spam. The managers here use moderation to keep most of it off the boards and consequently out of your e-mail if you elect to recieve posts by mail. What we can't control is what you may get from scumbags that "mine" group membership rosters. Only you can prevent this by hiding your e-mail on your group profile.
It is your profile. We have no rule requiring that you hide your e-mail on your profile, nor do we require you to read only on the web. We do however strongly recommend it.
To check your E-mail settings, make sure you are signed in and Click here. Teddie was nice enough to supply the following screenshot of our recomended settings. 
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