[exim] listed at .backscatterer.org

Hi,

One of my mail servers has been listed at backscatterer.org
They say they can remove me for 92 euros or I will be automatically removed
in 4 weeks.

It doesn't look like a RBL that can be used to block messages, more of a
list of mail servers that send bounce back messages.

I can see why the server was listed (I handle outbound email for some
companies, one of them sent a bounce back message via their inbound server,
through my server,
to a domain that was in reality a backscatterer monitor).

I don't think I should stop sending bounce backs as long as they are
legitimate (if for example somebody made a typing mistake when composing a
message).
But I do want to stop sending bounce backs to messages that didnt come from
where they say they did.

Is there a way to determine if I should send a bounce back message in a
particular instance?

I'm definitely not going to pay the 92 euros.

Thanks,

Oliver