"A DNS-based Blackhole List, or DNSBL, is a means by which an
Internet site may publish a list of IP addresses, in a format which
can be easily queried by computer programs on the Internet. As the
name suggests, the technology is built on top of the Internet DNS
or Domain Name System. DNSBLs are chiefly used to publish lists of
addresses linked to spamming. Most mail transport agent (mail
server) software can be configured to reject or flag messages which
have been sent from a site listed on one or more such lists.
"In this article, I'll discuss how you can configure sendmail
using DNSBL to block E-Mail Spam on a mail server running on Fedora
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