echo 'deb-src ftp://ftp.nl.debian.org/debian/ testing main contrib non-free' >> /etc/apt/sources.list
apt-get update
apt-get build-dep exim4 
apt-get install libspf2-dev libspf2-2
cd 
wget http://www.kibibyte.se/download/debian/libdomainkeys0_0.68-1_i386.deb
wget http://www.kibibyte.se/download/debian/libdomainkeys0-dev_0.68-1_i386.deb
dpkg -i libdomainkeys0_0.68-1_i386.deb
dpkg -i libdomainkeys0-dev_0.68-1_i386.deb
cd /usr/src
apt-get source exim4
cd exim4-4.68

fakeroot debian/rules unpack-configs
cp EDITME.exim4-heavy EDITME.exim4-custom
vi EDITME.exim4-custom

# uncomment next lines:
 EXPERIMENTAL_SPF=yes
 LDFLAGS += -lspf2
# add next lines
EXPERIMENTAL_DOMAINKEYS=yes
LDFLAGS += -ldomainkeys

fakeroot debian/rules pack-configs
fakeroot debian/rules extradaemonpackages=exim4-daemon-custom binary

ls ../*deb

#TEST:
cd ..
dpkg -X exim4-daemon-custom_4.68-2_i386.deb EXIM
ldd EXIM/usr/sbin/exim4  | grep -e domainkeys -e spf
        #libspf2.so.2 => /usr/lib/libspf2.so.2 (0xb7752000)
        #libdomainkeys.so.0 => /usr/lib/libdomainkeys.so.0 (0xb774c000)