A URI DNSBL is a DNSBL that lists the domain names and IP addresses which are found in the "clickable" links contained in the body of spams, but generally not found inside legitimate messages.
This antispam method scan submitted content for the urls and check them if any of them is a link to spam site. If such url detected in the text then content is not submitted.
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More info about URI DNSBL: <br />
<a href="http://www.surbl.org/">http://www.surbl.org/</a> <br />
<a href="http://dnsbl.invaluement.com/ivmuri/">http://dnsbl.invaluement.com/ivmuri/</a>