[exim] Problem compiling Exim with libdomainkeys

Hi, list!

I downloaded libdomainkeys-0.68 and compiled it.
Now I want to compile Exim against this library, then I wrote this in my
Local/Makefile:

# DomainKeys
EXPERIMENTAL_DOMAINKEYS=yes
CFLAGS += -I/opt/download/libdomainkeys
LDFLAGS += -ldomainkeys -L/opt/download/libdomainkeys

Of course, the libdomainkeys IS in /opt/download/libdomainkeys... :)

Now, by make of exim, I get:

gcc exim_dbmbuild.c
In file included from exim.h:450,
                 from exim_dbmbuild.c:33:
dk.h:15:24: domainkeys.h: No such file or directory
make[1]: *** [exim_dbmbuild.o] Error 1
make[1]: Leaving directory `/opt/download/exim/exim-4.67/build-Linux-i386'
make: *** [go] Error 2

I can't understand why it does not find this header...
Do you have an idea?

Thanks a lot
Luca Bertoncello
(lucabert@???)