[exim] Errors in transport filters

Hi all,

maybe this is a FAQ but I could not find an answer to my question.

I'm using this transport filter in Exim:

filter_transport:
driver = pipe
command = /usr/sbin/exim ...
transport_filter = /some/command ...
log_output = true
temp_errors = *
message_prefix = ""
message_suffix = ""
user = exim
group = exim
return_path_add = false

Sometimes the filter will fail due to the called script exiting with a
non zero exit code. In this case the message stays in the queue and exim
will try to deliver it with the next queue run. But exim sends the mail
nevertheless therefore the mail gets duplicated on every queue run.

How can I stop exim sending the additional mail? I want that the mail
will stay in the queue until it could pass the transport filter.

fs