[exim] Checking recipient and wildcard

I have a exim setup that is a redundant MX. The server accepts mail for
a list of domains and holds the mail until it can deliver it to the
primary server. The problem i'm having is that this server gets a ton
of spam because it's accepting mail for any recipient and then hammers
the primary server. I modified my check_recipient acl so that it has
the following

accept domains = +relay_domains
local_parts = lsearch;/etc/relaydomains/$domain
verify = recipient


Before it only had

accept domains = +relay_domains

This works great as long as i keep /etc/relaydomains/$domain updates but
the problem comes with some domains that have catchall type aliases. On
the primary server the aliases file has a *: catchall@domain entry.
With the modifications above if i add * to the /etc/relaydomains/$domain
it does not accept mail for all recipients.

Looking for ideas about what i need to do, thanks!

~ShaunR