[exim] Prevent bouncing

Hello.

I'm using Exim 4.63 with Debin 4.1.
This server is forwarding some email to remote domains and sometimes a few
messages are returned with 5xx errors. Quite often this happens because
the remote server considers the message to be spam.
I can not use a spam filter and refuse the messages on my server. I have
to try to forward all the email.

Is there any way I can avoid the bounce message that Exim will generate
but will never be delivered because the source does not exist?
I wanted to do something like:
if the server to which I forward email returned 5xx, discard (or frozen)
the message and don't bounce to the sender.

Thank you,
Marco