Rationale

To enable more in-depth filtering of Unknown mail

In-depth filtering is costly in terms of server processing. The more tests are performed on incoming mail the more the mail queue slows. If the volume of mail for testing can be reduced by eliminating from tests both the known bad mail and the known good mail, and only testing what’s left over, the volume of mail to test is significantly reduced and thus can undergo far greater in-depth testing.

To eliminate false positives in spam filters

Spam filters come in all shapes and from a myriad of suppliers. A rare few do a near perfect job but can not catch 100% of spam. Some catch a lot of spam but also an amount of good email. Some are very agressive, some are designed to block whole networks, some to block whole countries. Message content filters and in particular Bayesian “I think it’s spam” statistical filters too often wrongly tag good email as spam. There is no sense in passing known good email through such filters.

To automatically certify DKIM digital signatures

The domain element of the Spamhaus Whitelist, the Domain Whitelist (DWL), enables receivers to automatically certify DKIM digital signatures. The recipient now knows (A) that the message is really from the sender and (B) that the sender has been vetted as not a spam sender.

To protect important email communication

Transactional mail such as automated billing systems, ecommerce transaction servers, banking and online booking system mail, should be afforded special handling by mail servers to ensure these messages get through even the most agressive spam filter setups. Likewise, mail sent by banks, accounting firms, law firms, airlines, medical centers, government agencies, etc., should not be subjected to delay or false positive risk from multiple spam filters when the sender is known to be extremely unlikely to ever send spam. Important transactional mail from Expedia or Ebay for example goes through spam filters unnecessarily and with risk of being filtered into junk folders.

To tackle the problem of spam in IPv6

The arrival of IPv6 presents internet mail servers with a very significant new challenge. Once IPv6 mail starts flowing in ernerst, the volume of IPv6 spam – in particular the potential volume of sources that can send spam in IPv6 – risks overwhelming current filter technologies. Blocklists designed to store millions of bad IP addresses suddenly need to cope with potentially many billions of bad IP addresses. Yet legitimate mail servers in the world number only a few hundred thousand. It thus becomes sensible to identify and single out the few hundred thousand to let past unimpeded.

To assist scoring filters

Although Spamhaus advises that mail from whitelisted IPs or domains should be allowed straight past spam filters, some mail server adminitrators may still ‘not trust anyone but themselves’ and want to test all mail for spam. In these cases the whitelist can at minimum help reverse negative scores assigned by scoring systems due to presence of banned words, HTML or other factors in the mail.

THE SPAMHAUS WHITELIST

The Spamhaus Whitelist allows mail servers to separate incoming email traffic into 3 categories: Good, Bad and Unknown.

For recipients, the Spamhaus Whitelist heralds an end to messages marked by error as spam by scoring systems and content filters. For email senders, it means an end to important mail lost in junk folders, delayed or wrongly filtered as spam. For transactional mail, such as ecommerce systems, banking, airline booking, mail from medical centers, judiciary or government agencies, it means mail arrives no matter how heavily filtered the receiver's mailbox is. With the Spamhaus Whitelist email becomes truly reliable.