Do not use free public DNS servers like Google DNS, OpenDNS or Level3 for nameservers in your servers
/etc/resolve.conf as some DNS blacklists and whitelists will block queries from DNS servers issuing what they consider too many queries. This means that some of the tests that SpamAssassin will try to perform will be blocked and non-functional.
If your DNS servers are getting blocked you will also see URIBL_BLOCKED in the Warden spam log when you click on a spam row:
0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [URIs: i44hosting.com]
Spamassassin 3.4.0+ allows you to set which DNS servers it will use for DNS lookups. If your DNS servers are getting blocked we recommend that you set non-free DNS servers under:
Warden -> Settings -> Network Settings -> DNS servers