[exim] Accepting mail for remote networks

Hi

I currently have a layer 4 transparent redirection of all MX mail whose
MX's belong to a particular network (eg 1.1.1.0/24), redirected to our
Exim servers.
So any domains whose MX records have its A records in 1.1.1.0/24 will be
relayed for.
The reason for this is that i do not know what domains our exim servers
will be relaying for but i do know the remote network - which we control.
I am currently doing this check in the Rcpt To ACL by checking the MX
record for the remote recipient domain and then the A record, using dnsdb.
I then have a condition which basically checks to to see if the resolved
IP is in the remote network and denys or allows the mail appropriately.

Is there any better way of doing this?

Thanks,
Warren