[exim] E-mail forwarders

My apologies if this message is double posted, but I neglected to send
it from the correct e-mail address, and I assumed that this would mean
it would be rejected.

I have a server that runs DirectAdmin running Exim 4.60.

My question pertains to e-mail forwarders. I tried to resolve the
issue on DirectAdmin's forums but it seemed to be out of the scope of
those forums.

The issue I am experiencing is that many of my clients have e-mail
forwarders setup for their domains. My server will receive an e-mail
message, then redirect it to their forwarded e-mail address. What has
happened quite often is that their forwarded e-mail address is
filtered by Barracuda servers. If the original message is then
detected as spam by their Barracuda servers, *my* server is then
flagged as a source of spam, which eventually causes all e-mails sent
my any of my clients to be filtered/blocked by any Barracuda servers.

My question is basically this: is there any way to prevent this?
Whether it is somehow "silently" redirecting the message (without
leaving any record that my server touched it), or some other way of
basically not having my server appearing to be the spam source?
Otherwise, I feel my only other solution is to simply disable forwards
altogether, as having to constantly reset my Barracuda "reputation" is
annoying to me, but also very inconvenient to my clients who wonder
why their e-mails do not get through.

This is how the forward is setup by DirectAdmin:

virtual_aliases_nostar:
driver = redirect
allow_defer
allow_fail
data = ${if exists{/etc/virtual/${domain}/aliases}{$
{lookup{$local_part}lsearch{/etc/virtual/${domain}/aliases}}}}
file_transport = address_file
group = mail
pipe_transport = virtual_address_pipe
retry_use_local_part

/etc/virtual/domain.com/aliases is a file that contains the forwarded
e-mail addresses. I'm not sure if this setup makes references to
other parts of the configuration — I'm not an Exim expert in any sense
of the word, so if someone needs additional items from my exim.conf,
please let me know.

Thanks for any help.

-Andrew