When you go into the group itself, on the far right when you scroll down there are a list of options.
Home - Matches - members - Forums - Alerts - News
If you click on Alerts, it shows you the types of alerts you can receive from that specific group. UN-checking the boxes then save changes will stop unwated alerts from that group.
You shouldn't receive alerts from any group you're not a member of unless its another member asking you if you wish to join.
How do I manage what messages I receive?
How do I ensure I receive messages and alerts only from the groups of which I'm a member?
It says that I can do it from 'Group Settings' but I can't see how.
Thanks
Jo