How do stop steam group news pop up?

Umm.. Leave from unnecessary group ?

When i play, to avoid those pop-up, i just didn't go online (set status to offline) or turn of steam overlay..

i'`m asking the same question :( , the spam it's soo anoying

you can't setup group and friends notifications separately. So either you comletely disale it at all or you get it all

Fight fire with fire and spam them back. SPAM WARS V: A New Hope

you can't. it seems it's a "feature" by valve and unless you leave those groups, you will get all the spam nonstop. :3