Mar 18th, 2012
Understanding DNSBL Filtering
Understanding DNSBL Filtering
A DNSBL (commonly known as a ‘Blocklist”) is a database that is queried in realtime by Internet mail servers for the purpose of obtaining an opinion on the origin of incoming email. The role of a DNSBL such as Spamhaus’ SBL/XBL/PBL Advisory system is to provide an opinion, to anyone who asks, on whether a particular IP Address meets Spamhaus’ own policy for acceptance of inbound email.
The policy of the Receiver governs whether a message is blocked or not
Every Internet network that chooses to implement spam filtering is, by doing so, making a policy decision governing acceptance and handling of inbound email. The Receiver unilaterally makes the choices on whether to use DNSBLs, which DNSBLs to use, and what to do with an incoming email if the email message’s originating IP Address is “listed” on the DNSBL. The DNSBL itself, like all spam filters, can only answer whether a condition has been met or not.
