[exim] Sending from outlook when IP is in spamhaus PBL

Hi,

I have a problem whereby I have a check connect ACL using Spamhaus
dnslists, and I have a user who is trying to send from an mail client
via SMTP. The users IP is within the range blocked by Spamhaus here:

http://www.spamhaus.org/pbl/query/PBL231588

I had a go adding a line to accept authenticated connections, but Exim
threw me back an error saying "cannot test authenticated condition in
connection ACL". So I'm just wondering if there is anything else I can
do, other than have mail go via BT mail servers.
Any ideas appreciated,

thanks Andy.