Untangle provides powerful SPAM protection via the SPAM filter rack module. Using this powerful tool, admins can effectively block the majority of SPAM threats to their network. One of the powerful features of this rack module is the SPAM tarpitting functionality. When you enable tarpitting, it enables the DNSBL, or “blacklisting” of known SPAM IP addresses via the zen.spamhaus.org DNS zone.
In working with a client recently who used the Untangle SPAM filter and enabled tarpitting, they had noticed that the tarpitting functionality had stopped working. In searching message boards and the Untangle wiki and forum sites, the reason that kept popping up for tarpitting not functioning correctly was using a public DNS server. Sure enough in checking the DNS settings for the network, recent changes had enabled the Google 220.127.116.11 DNS server value in one of the forwarder values for DNS. Shortly after this change was made, the tarpitting function had stopped working and SPAM was being passed albeit much of it quarantined instead of being blocked.
After making the change to disable the public DNS server value, Untangle once again started utilizing the tarpit function in effectively blocking known SPAM addresses via the DNSBL listings.
****Note***** It may take some time after making the DNS change for tarpitting to start working again.