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DNSBL / RBL Services (DNS BlackList or DNS Blackhole List or Realtime Blackhole List) A system for identifying spammers based on their IP addresses. Most mail servers are able to query a DNSBL to determine if a specific IP address is on the list.
DNSBL/RBLuses the DNS protocol to query the well-known IP addresses which have been complaint to send worm, virus & junk mail. Using RBLs to prevent junk, virus & worm email is very effective. The algorithm of RBLs is different with that of Anti-Spam and Anti-Virus services as RBLs works based on IP address, while Anti-Spam and Anti-Virus services work based on the message content.
The RBL-DNS (RBL) utilizes a standard DNSBL (Domain Name System Block List) implementation that can be used to reduce spam volume on many popular email systems. DNSBL systems list IP addresses, often those that have been observed by the list operator to be sending spam or hosting spammers. By adding DNSBL entries to an email server configuration, those email servers can either reject connection attempts from listed IP addresses or use that listing to apply appropriate filtering policy.
It is important to note that a DNSBL cannot stop anyone from sending email. A DNSBL only prevents delivery at the receiving end at the receiver's instruction. DNSBLs are strictly defensive tools, and they cannot do any offensive damage such as denial of service attacks.
SURBL is an abbreviation for Uniform Resource Identifier Blacklist. A SURBL lists domain names that appear in URIs such as web sites mentioned in message bodies. This is similar to a DNSBL but it lists domain names rather than IP addresses.
The DNSBL / RBL can be queried directly as bl.rbl-dns.com
Currently, the following zones exist:
- bl.rbl-dns.com combination of spam.rbl-dns.com and dul.rbl-dns.com in a single zone.
- spam.rbl-dns.com (Open Relay, Hijacked PCs, Spam Source)
- dul.rbl-dns.com (Dynamic, ADSL, Cable, no PTR Networks)
Doing a DNSBL lookup on a message at SMTP connect time is cheap in hardware cycles and system time. Your DNS server may even have it cached from the last time the spammer tried.
Mail rejected by a DNSBL during delivery is not silently discarded or lost. A DNSBL realtime rejection creates a delivery status notification to the sender identifying the cause of the rejection, thereby allowing troubleshooting on the sender's end.
By rejecting the connection attempt in real-time, a DNSBL also avoids any problems associated with an email system accepting delivery, closing the connection, and then trying to return the mail to a potentially forged address after the message is determined to be spam.
DNS is inherently very efficient, using minimal amounts of bandwidth. Using BL will use much less bandwidth than having to accept every spam and virus email sent to your email system. By rejecting these spam messages during the SMTP connection, no further data is sent thereby reducing overall bandwidth requirements. DNS caching by your local DNS server also prevents redundant queries from utilizing excessive bandwidth.
The use of the RBL-DNS DNSBLs is free of charge for low-volume non-commercial use.
For professional use, internet ISPs, or hosting providers, we can provide your unlimited or dedicated realtime access to all RBL-DNS DNSBLs from your network.
Free mirror service is provided to sites who are willing to host a public mirror (serving data to other free users).