No "New Mail"-Sound in Mail since upgrade
I have the same issue as this guy
Notifications for Mail after upgrading to El Capitan not working
OF COURSE I COULD REPLY THERE, if not the side or Safari was bugged
and no "reply", "I have the same problem" or "reply to the original post" worked.
I tried several things like turning it off and on again in Notifications or Mail itself,
but it does simply not work.
Cheers