[EXIM] Why doesn't this system filter work?

I tried to make a system filter that sends copies of all emails from certain
users to other addresses, but I can't get it to work:

# Exim filter <- do not edit or remove this line

if first_delivery then
  if "${lookup {$sender_address} dbm {/var/exim/etc/bcc.db} {true} {false}}" is "true" then
    unseen deliver "${lookup {$sender_address} dbm {/var/exim/etc/bcc.db} {$value} fail}"
  endif
endif

At run time, I get this:

1999-06-15 17:51:39 10tvUr-0000mF-00 <= michael@mydomain H=[myip] P=smtp S=300 from <michael@mydomain> for michael@???
1999-06-15 17:51:39 10tvUr-0000mF-00 == michael-2@??? <message filter> T=t_extern defer (-1): domain matches queue_smtp_domains, or -odqs set
1999-06-15 17:51:39 10tvUr-0000mF-00 == michael@??? T=t_extern defer (-1): domain matches queue_smtp_domains, or -odqs set
1999-06-15 17:51:45 10tvUr-0000mF-00 => michael@??? D=d_smtproute T=t_extern H=mout.mydomain [myip] C="250 OK id=10tvV3-00086v-00"
1999-06-15 17:51:45 10tvUr-0000mF-00 Completed

And that's it. michael-2@???, which was generated by the filter,
appears to be lost. Why? I am using Exim 3.02.

Michael

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