This is a guide to install DKIM on CentOS 5 mail servers using qmailtoaster and Kloxo panel:
wget http://software.atnerds.com/linux/dkim/dkim.tgz
tar –zxf dkim.tgz
cd dkim
yum install perl-XML-Simple perl-Mail-DKIM perl-XML-Parser rpm-build openssl-devel
wget http://software.atnerds.com/linux/dkim/libdomainkeys-toaster-0.68-1.3.6.src.rpm
rpmbuild --rebuild libdomainkeys-toaster-0.68-1.3.6.src.rpm
rpm -ivh /usr/src/redhat/RPMS/i386/libdomainkeys-toaster-0.68-1.3.6.i386.rpm
mkdir /var/qmail/control/dkim
cp signconf.xml /var/qmail/control/dkim/
chown -R qmailr:qmail /var/qmail/control/dkim/
dknewkey /var/qmail/control/dkim/global.key > /var/qmail/control/dkim/public.txt
perl -pi -e 's/global.key._domainkey/dkim1/' /var/qmail/control/dkim/public.txt
qmailctl stop
mv /var/qmail/bin/qmail-remote /var/qmail/bin/qmail-remote.orig
mv qmail-remote /var/qmail/bin
chmod 777 /var/qmail/bin/qmail-remote
chown root:qmail /var/qmail/bin/qmail-remote
qmailctl start
Create a TXT record dkim._domainkey.domain on DNS server for the
domain you want to set DKIM as shown in the output of the following
command
cat /var/qmail/control/dkim/public.txt
DKIM setup should be finished. Once the DNS updates, you should be able to send DKIM signed emails.