The only people who like spam are spammers, and they like it because it makes them money. Hundreds of billions of spam emails are sent every day. If there was no way to stop spam reaching users, email would be essentially useless. The noise would far outweigh the signal.
To stop spam being delivered, there are many layers of filtering between sender and receiver; from filtering by email providers and third-party filtering like that provided by MailChannels; to the spam recognition and filtering mechanisms included in modern email clients.
DNS blacklists—also known as blackhole lists—are part of the internet’s immune system. They help email inbox providers, ISPs, and other organizations stop spam before it reaches their users.
DNS blacklists can be created by anyone. Many network administrators and inbox providers maintain private lists of IP addresses their email systems won’t deliver. Third-party blacklists are created and managed by specialist organizations, including SpamHaus and SpamCop. ISPs and other organizations that deal with a lot of incoming email don’t want to have to maintain huge and up-to-date blacklists internally, so they outsource the problem by subscribing to third-party blacklists.
The best way to avoid being included in a blacklist is to ensure your organization’s outgoing mail doesn’t include any spam. But because spam is such a huge problem, blacklist maintainers can have a trigger finger when it comes to including IP addresses in their lists. That presents a problem for email providers and other organizations that rely on having their email delivered.
The organizations that maintain blacklists “work for” the ISPs and inbox providers, who really don’t like it when spam gets through to their users. They don’t work for the organizations who send email. That means the incentives of blacklist providers are usually tilted towards a “block and ask questions later” approach. If they think that quantities of spam above a certain threshold originate from an IP or block of IPs, they will add those IPs to a blacklist — they don’t care whose fault it is.
Once an IP is listed on a blacklist, it is possible to have it removed, but it can be a lot of work. The blacklist maintainers would rather keep false positives in their list than let spam through, because their loyalty is to their subscribers, not email senders. That said, most reputable blacklist providers want to maintain accurate lists.
Being blacklisted is a risk for any organization that sends email, and the only real solution is to proactively monitor your organization’s outgoing email to ensure it doesn’t include spam. If spam isn’t getting through to email inbox providers, large organizations, and ISPs, the reporting mechanisms that lead to email being included in blacklists won’t be triggered.