What does "ja" do in this sentence?
So is it supposed to express something like: "Well obviously, otherwise you cannot forward it!" ?
I suppose so. It's meant as emphasis. Something like "Otherwise, one can't pass it on, right!?" Or duh! - although I'm sure that's more rude.
Can someone please explain why my answer was not right?
- On the other hand, one cannot pass it on!
"sonst" doesn't mean "on the other hand".