[Exim] transport preserving the envelope

Hi everybody,

I have my exim configured to first lookup some aliaslists that lookup
mail adresses and alias them to local mailbox names, such as

martin@???    localBox1

Afterwards, the mails are sent to a transport that calls the Amavis
virus scanner. This transport changes the envelope recipient (RCPT TO)
from martin@??? to localBox1@???

amavisTransport:
driver = pipe
command = "/usr/local/sbin/amavis -f <${sender_address}> -d ${pipe_addresses}"
prefix =
suffix =
check_string =
escape_string =
return_output = true
return_path_add = false
user = mailnull
group = mail
path = "/bin:/sbin:/usr/bin:/usr/sbin"
current_directory = "/var/log/amavis"


This causes problems with some of our customers. Is there a way to
configure the transport to preserve the envelope recipient??

Thanks for your help,

Martin