[exim] No bounce for spam.

Hi, mighty list...

My situation is as follows:
I have a antispam system which forwards all messages to exim, if a
message is spam, antispam system adds
"X-Spam: YES" header. If message contains "X-Spam: YES" header,
meaasge is put into "Spam" inbox, which can be eventually checked by
end user.
But lot's of messages as passed to exim (messages with "X-Spam: YES"
header) and then bounced back.
All I want to do is to stop bouncing if message is "X-Spam: YES".

And, the question is: how to achieve that.

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Cheers,
Paweł 'zeddi' Zadrąg - The IT Staff