Editing Domain Name System blocklist (section)

=== URI DNSBLs ===
A [[Uniform Resource Identifier]] (URI) DNSBL is a DNSBL that lists the domain names and sometimes also IP addresses which are found in the "clickable" links contained in the body of spams, but generally not found inside legitimate messages.

URI DNSBLs were created when it was determined that much spam made it past spam filters during that short time frame between the first use of a spam-sending IP address and the point where that sending IP address was first listed on major sending-IP-based DNSBLs.

In many cases, such elusive spam contains in their links domain names or IP addresses (collectively referred to as a URIs) where that URI was ''already'' spotted in previously caught spam and where that URI is not found in non-spam e-mail.

Therefore, when a spam filter extracts all URIs from a message and checks them against a URI DNSBL, then the spam can be blocked even if the sending IP for that spam has not yet been listed on any sending IP DNSBL.

Of the three major URI DNSBLs, the oldest and most popular is '''[[SURBL]]'''.<ref>{{cite web |url=http://www.surbl.org/ |title=SURBL |publisher=SURBL |access-date=2012-05-06}}</ref> After SURBL was created, some of the volunteers for SURBL started the second major URI DNSBL, '''URIBL'''.<ref>{{cite web |url=http://www.uribl.com/ |title=URIBL |publisher=URIBL |access-date=2012-05-06}}</ref> In 2008, another long-time SURBL volunteer started another URI DNSBL, '''ivmURI'''.<ref>{{cite web |url=http://dnsbl.invaluement.com/ivmuri/ |title=ivmURI |publisher=Dnsbl.invaluement.com |date=2008-05-31 |access-date=2012-05-06 |url-status=dead |archive-url=https://web.archive.org/web/20120505190857/http://dnsbl.invaluement.com/ivmuri/ |archive-date=2012-05-05}}</ref> [[The Spamhaus Project]] provides the Spamhaus Domain Block List ('''DBL''') which they describe as domains "found in spam messages".<ref>{{cite web|url=http://www.spamhaus.org/dbl/ |title=The Domain Block List |publisher=The Spamhaus Project |access-date=2014-10-10}}</ref> The DBL is intended as both a URIBL and RHSBL, to be checked against both domains in a message's envelope and headers and domains in URLs in message bodies. Unlike other URIBLs, the DBL only lists domain names, not IP addresses, since Spamhaus provides other lists of IP addresses.

URI DNSBLs are often confused with RHSBLs (Right Hand Side BLs). But they are different. A URI DNSBL lists domain names and IPs found in the body of the message. An RHSBL lists the domain names used in the "from" or "reply-to" e-mail address. RHSBLs are of debatable effectiveness since many spams either use forged "from" addresses or use "from" addresses containing popular free mail domain names, such as [[gmail.com]], [[yahoo.com]], or [[hotmail.com]] URI DNSBLs are more widely used than RHSBLs, are very effective, and are used by the majority of spam filters.