In classic Yammer, in the right rail of every group, you had an 'Admin' section - which enabled you to set a group activity email notification, or email into the group.
My network is still on classic Yammer, but I'm able to preview new look Yammer by going to web.yammer.com.
When I look in a community, I don't see the admin section any more. Does this mean the only way a user can set a group activity email is by going to cog > edit settings > Notifications tab > then ticking the boxes next to the groups? I hope there's an easier way than this!