Blacklists have been around for over two decades, meaning that blacklists (blocklists or deny lists) existed before most humans were on the Internet. The goal of blacklists is to remove Spam email from the Internet, however, the implementations and algorithms vary dramatically. A few of examples:

• Spamhaus ZEN CBL reports the IP address of sources of email that have been infected with Viruses or Malware. Even if your email was not used for spam, your computer could be.
• NoSolicitado reports sources of Spanish language spam. There are many other language-based blocklists.
• CASA CBL reports source of spam received by the China Anti-Spam Alliance.
• FABELSOURCES reports entire networks that are the source of spam. There are several similar lists, including UCLPROTECTL2 and L3.
• Open-Relays Verifying Engine Database List (ORVEDB) lists IP numbers of hosts that the Open-Relays Verifying Engine (ORVE) verified that are Open-Relays machines. Open relays are basically a purposeful or accidental email server misconfiguration that promotes spamming.
• The Abusix Domain Blacklist contains domain names that have been identified being used in spam, phishing, or malware. Note: There are very few actual domain blacklists so the MxToolbox SuperTool also checks the IP address in the A record for the domain to see if the server has been compromised.

The Topic of Coin – How do Blacklists Make Money?

Early on Blocklists were free subscriptions for anyone to use to help reduce spam email to their servers. Since the lists were small, these were setup to be shared via FTP and then as the lists grew bigger via Realtime DNS. Many smaller blacklists are still free to query.

Eventually, security companies started to develop their own proprietary Blocklists or Deny Lists and integrate these into network appliances like firewalls, routers or email gateways. The primary economic model for blacklists is to sell their data to security-focused companies and automatically maintain the lists through remote syncing data feeds. Security services then update their hardware and software email filtering to include these lists. Often, weighing each blacklist differently but sometimes using them as a binary filter – if the sending IP is listed, deny the email.

Do blacklists charge for delisting?

MxToolbox recommends that you should never, ever pay to be delisted. All legitimate blocklists have a free method of delisting, that while sometimes slow, is still free. Fix the problem that caused you to be listed and wait it out. Delisting usually takes a week or so depending on the blocklist.

There are both for-profit and non-profit blacklists. For-profit blacklists make money by selling their lists to security companies or security minded companies for use in their products. For example, MxToolbox purchases subscriptions to some blacklists to enable our customers to lookup their blacklist status in the SuperTool.

Non-profit blacklists offer the option to donate to support them. This should never be conditional on the delisting of the IP address.

Some blacklists may offer an expedited delisting option for a fee. Sometimes this might seem like an enticing option, but, remember, MxToolbox does not recommend paying for delisting. It is your decision to pay, however, we have a few considerations:

• Have you fixed the issue causing you to be classed as spam? If you have not fixed the issue causing you to be listed, you will be re-listed almost immediately. Paying doesn’t fix your systems or cause you to be whitelisted.
• Do you do own the network? If you don’t own the entire network, in the case of a network or ASN listing, then you can’t stop your network or ASN neighbors from getting the entire network re-listed. It’s best to contact the network owner, ISP, datacenter provider, etc.
• Has being blacklisted affected your email deliverability? If not, then you can wait it out. If so, then how many emails were affected? Is a small email delivery problem worth the expense?
• Are you ready to be treated like a spammer? Blocklists with expedited pay setups sometimes assume that anyone willing to pay is a spammer. Spammers make all their money from email, so a block is potentially fatal. Legitimate businesses have other methods of customer communication. Paying could get you additional scrutiny in the future.
• Is your IP address on multiple blacklists? If you are listed on multiple blacklists, do you want to pay multiple times or wait it out? Can you even pay to delist from all of the blocklists? Multiple listings means a serious problem, so we recommend taking care of the issue and waiting for delisting.

How do you prevent being blacklisted?

There is no one simple way to prevent blacklisting. Owning your own email servers requires constant adjustment and maintenance to prevent your systems from being used for spam or perceived as spam. Outbound email filters can help, but many companies, large and small are abandoning the idea of hosting their own email and adopting 3rd party email senders to improve email delivery. Google Workspace, Microsoft Office365, Yahoo!, Mailgun, Constant Contact, MailChimps, etc. all offer reduced risk of blacklisting by spreading email out over a large network of sending IP addresses and providing outbound email filtering.

New Technologies – DMARC, DKIM, SPF

Email delivery technologies are rapidly changing and the key to good email deliverability is actively managing your online reputation. Blacklisting is just one piece of the puzzle. SPF, DKIM and DMARC are now the most important factors at getting your email to the inbox. These technologies help identify you as the owner of the email and enable you to elicit feedback from Inbox Providers about problems with your email.

To maintain the highest levels of email deliverability using DMARC, businesses like yours need a proven Email Delivery management system like MxToolbox Delivery Center.  Delivery Center provides you with valuable insight into your email delivery posture and the ongoing maintenance necessary to maintain peak performance:

• Manage SPF, DKIM, and DMARC (and BIMI) to improve compliance and reduce the threat of fraud and phishing using your domain.
• Review daily volume and SPF, DKIM, and DMARC compliance rates to ensure the best email deliverability.
• Implement Feedback Loops to gain unique information on how your recipients view your emails and when they mark you as spam.
• Gradually move your DMARC policy to Reject to enable better inbox placement opportunities and reduce the risk of Phishing and Fraud using your domain.
• Manage the on-going requirements of maintaining high levels of email deliverability