[exim] Problem with match expansion

Hi,

I'm trying to check in an acl wether the sending host is a mx for the
domain. To test, I have tried this:

message = X-HostIsMX: ${if match{${lookup dnsdb{>: a=${lookup dnsdb{>: \
mxh=$domain}}}}}{$sender_host_address}{yes}{no}}

But this won't work. But if I try:

message = X-Test: ${lookup dnsdb{>: a=${lookup dnsdb{>: mxh=$domain}}}}

and I manually insert the output from the X-Test header into the first
one, like this:

message = X-HostIsMX: ${if match{87.248.7.17:80.203.232.75}\
{$sender_host_address}{yes}{no}}

it works perfectly.

Is there any reason this should not work?

Best regards,
Stian