Google groups has provided a very nice and clear system to report a Group but Yahoo sometime is annoying and it is difficult to find the Group abuse report page. Often it happens with me suddenly I start reciving tons of email in my inbox. When I inquire about the sender I came to know these email coming from various mailing groups, mostly Yahoo groups. I have a yahoo identity and I am part of few yahoo groups too, but when I visited my yahoo groups page I don't find myself as a member of group who is sending me bulk emails. This thing really irritating me. When I visit suspected group who is sending me un-necessary email I can't login to that. I have added my multiple ids in my yahoo groups setting so most of the time I transfer my regular group emails to gmail or hotmail becuase I can't bother login to all my mail boxes everyday. This confuses me more at Yahoo groups.
How to Report a Yahoo GroupTo report abuse of a Yahoo group please visit the url below.
http://help.yahoo.com/abuse or abuse.yahoo.com
You will find a page like this. (click on the image for a larger version)
Select Group Abuse, you will be presented a form where you have to fill out, your contact details, group name, the email you found from group including full header.
After filling out all these details, just sit back and relax. Yahoo customer support team will soon take necessary actions on that and they probably contact you once or twice in case they need more information.
If you have something to ask, please drop me a comment and I'll response back soon. I hope this information will be useful for you.