According to perldoc /usr/share/qpsmtpd/plugins/dnsbl there is a config file 'dnsbl_allow' that exempts IP addresses from dnsbl checks.
Looking at /etc/e-smith/templates/var/service/qpsmtpd/config/dnsbl_allow, it looks like this file only contains the local networks.
If I'm right, you can exempt an external IP as follows (replace 10.10.10.1 with the IP you want to allow):
mkdir -p /etc/e-smith/templates-custom/var/service/qpsmtpd/config/dnsbl_allow
cd /etc/e-smith/templates-custom/var/service/qpsmtpd/config/dnsbl_allow
echo '10.10.10.1' > 99CustomIPs
expand-template /var/service/qpsmtpd/config/dnsbl_allow
sv t qpsmtpd
Un-do with:
cd /etc/e-smith/templates-custom/var/service/qpsmtpd/config/dnsbl_allow
rm -f 99CustomIPs
expand-template /var/service/qpsmtpd/config/dnsbl_allow
sv t qpsmtpd