What are DNS blacklists?

What are DNS blacklists?

DNS blacklists are lists of domains that are known to originate Spam. Many anti-spam software

programs use these lists to control Spam by refusing any email that originates from one of these

domains. DNS blacklists are usually maintained by anti-spam organizations or by individuals with

an intense dislike for Spam. The difficulty with DNS blacklists is the need for objectivity in

deciding when to blacklist a domain. In order to know that a domain is producing Spam, the offence

must be reported. Reporting Spam without any anti-abuse mechanism in place, however, leaves

nothing to stop people from getting servers added to a DNS blacklist out of malice. The obvious

solution would be to require a minimum number of reported incidents before blacklisting a server.

This proves equally unsatisfactory however as a measure to stop Spam mail. Anyone who manages

large mailing lists knows that a small percentage of people who subscribe subsequently accuse the

sender of spamming them when they receive their email. Naturally, a company that sends out

millions of legitimate commercial emails will receive more accusations of Spam than one that sends

out a smaller amount of spam free bulk email.

The real solution lies in good management. A system administrator that knows about Spam, that

knows who the large legitimate bulk mailers are and responds rapidly to complaints from unjustly

blacklisted domains will ultimately provide a useful service to the Internet community at large.

There are some well-managed DNS blacklists on the Internet and these can be a useful addition to

the feature set of anti spam software.