Tag Archives: blacklists

Why Email Deliverability Tools Fail Businesses

Email deliverability is a broad category of tools designed to help your organization get your email messages to your intended recipients. Subcategories of tools include:

  • TLS Reporting
  • MTA-STS Reporting
  • Blacklist monitoring
  • DMARC Compliance Management and Reporting
  • Inbox Placement Analysis
  • Email Warming
  • Google Postmaster and other Feedback Loops

Clearly, there is a lot to unpack here, and that’s the start of why many tools fail their business customers: too much complexity.

Complexity

The landscape of email deliverability solutions is very complex. Most vendors focus on a narrow area of email delivery. Take a few different examples:

  • DMARC Management and Reporting is a maturing specialty market with a large number of providers often offering only DMARC and nothing more.
  • Blacklist solutions market has been around almost 20 years with only a few specialty tools with blacklisting becoming less of a hindrance due to the use of mass cloud-based emailers.
  • Email Warming is a highly niche market with few entrants as cloud-based email solutions reduce the need for much of it.

This level of complexity can mean a business either needs to adopt multiple solutions or miss out on some of the functionality they need to manage email deliverability. A full email deliverability suite will allow management and reporting of the most important layers of email deliverability:

  • Blacklist Monitoring and Management
  • DMARC Compliance Management and Reporting
  • Inbox Placement Analysis
  • Google Postmaster and other Feedback Loops

Organizational Ownership

There are a few major business cases driving adoption of email deliverability technologies:

  • Protecting the brand from being used in fraud and phishing, usually driven by IT Security
  • Improving email delivery rates to increase downstream email metrics including sales.
  • Meeting Google, Yahoo and Microsoft bulk sender requirements to keep access to their inboxes.

Typically, Marketing drives the last two use cases. While IT and Marketing both have reasons to improve email deliverability, coordination is required for both of them to achieve value. Marketing owns the sales outcomes and will drive much of the adoption of email deliverability tools, but IT will end up implementing many of the underlying technologies, including SPF, DKIM and DMARC DNS entries. Lacking tools for both Marketing and IT to achieve their goals is another way email deliverability tools fail businesses.

What “delivery” actually means

Unfortunately, there are multiple very specific definitions around email delivery, and they differ from the popular idea of what it means for an email to be delivered.

  • Delivery – Technically, an email is considered delivered when the receiving server accepts the email from the sending server. This means a complete SMTP negotiation of the email payload via accepted TLS encryption. Most email is rejected at the server if not properly encrypted.
  • Quarantine Delivery – Many systems will accept an email, run email filtering algorithms and place the email in a quarantine box that only IT email administrators can access.
  • Spam/Junk Folder Delivery – Specialized algorithms at inbox providers like Google, Yahoo and Microsoft sift through incoming email for compliance with content and reputation rules, including algorithms that compare content to known spam content.
  • Inbox Delivery – This is the holy grail for email delivery and what most people assume “delivery” means. In fact, Inbox Delivery only occurs if the email passes many tests.

Since final inbox delivery is not guaranteed, email deliverability tools need to measure Inbox Placement in addition other email delivery metrics.

Email Deliverability is a Moving Target

Email is an ever-changing landscape attempting to balance accepting important correspondence while blocking unwanted or harmful email. Since the first days of email, spam has been a threat to inboxes. Back then, spammers setup their own email servers and broadcast from static IP addresses giving rise to IP-based blacklists. Then, specific domains were known to send spam, so domain-based blacklists were created. Now, spammers can setup and teardown email servers programmatically making spoofing easy while avoiding blacklists. DMARC forces those spammers to step through a few additional compliance hoops and ensures that they can’t use imitate legitimate domains. Now we have proprietary content algorithms for inbox placement. In the future, there will be additional AI-driven acceptance criteria to combat AI-based spam, spoofing and other malicious email. The arms-race is constantly evolving so email deliverability tools must as well. Businesses lose out if they are not subscribing to email deliverability tools that are also constantly evolving.

How MxToolbox Helps

MxToolbox has over 20 years of experience in Email Deliverability technologies. Starting from basic DNS lookups to help IT admins setup email servers, we have constantly improved our free tools and paid email delivery solutions to meet the constant changes in the market. At MxToolbox.com, you can get free TLS Report, MTA-STS, SPF, DKIM, DMARC and Blacklist lookups.

Our paid suite, MxToolbox Delivery Center provides everything you need to manage your email delivery through its constantly changing requirements. We provide:

  • Adaptive Blacklist Monitoring
  • DMARC Reporting and Management
  • Inbox Placement Analysis
  • Feedback Loop integration including major vendors and Google Postmaster reporting.

In addition, we have a team of experts that can provide a Managed Services approach to email delivery. We can take over or simply assist you with improve your email deliverability, managing your adoption of DMARC and other email deliverabilty issues.

Domain Reputation – Google’s Hidden Blocklist

Inbox Providers like Google, Yahoo! and Outlook.com are constantly evolving new ways to ensure that the email making their inboxes is safe, timely and relevant to their users. At their disposal are multiple layers of email technology protection:

  • TLS Encryption for connection
  • Blacklists (both internal and external)
  • DMARC Compliance (SPF Authentication, SPF Alignment, DKIM Alignment)
  • Spam Content Scoring Rules
  • Bulk Sender Spam Reporting Rules
  • Individual Spam/Junk Rules

In past blogs, we’ve discussed each of these layers, including Google’s Content Reputation checks. Today, we’ll discuss what we know about Google’s proprietary blocklists.

Blocklists come in two forms:

  1. A list of IP addresses that have sent spam or dangerous emails or should not be sending email at all.
  2. A list of Domains that have been used in fraud, phishing or spam emails.

Google employs both types of blocklist to limit the risk of spam email making their Inboxes. But, how does Google determine what IP addresses and domains to block?

Google’s Blocklist Logic

Traditional blocklists use a variety of methods to determine what IP addresses or Domains are threatening. Often these include networks of spam traps, honey pots and feedback from inbox owners. Google appears to leverage both commercially available IP blocklists and their own proprietary logic. Staying off a commercial blocklist is therefore the first step in making the Google inbox.

Google has access to more inbox data than any other Inbox Provider. They can leverage Customer Sentiment and Behavior to create an aggregate picture of incoming email from an IP address or domain. This works in a few ways:

  • Email from IP addresses that were marked as spam gives that IP address a negative reputation. Google tracks the ratio of those emails received to those marked as spam. Over a certain threshold, this sentiment causes the IP address to be blocklisted for all senders from that IP.
  • Email domains are similarly tracked across all inboxes. Over a certain threshold of users marketing the email as spam, all email from that domain will be marked as spam.
  • Email containing content that is similar to content from blocklisted IP addresses or domains is automatically placed in the spam folder.
  • Email domains with a persistent poor reputation maybe placed on a complete blocklist and fail delivery entirely.

How can you stay off Google’s Blocklists?

Staying off of Google’s Blocklists is similar to staying off any blacklist, with a few additional considerations:

  1. Maintain good email list hygiene. Remove old and unreactive email addresses to reduce the risk of being marked as spam.
  2. Use an email marketing service that spreads your sent email over multiple dedicated IP addresses for marketing campaigns. This reduces the risk of IP blacklisting.
  3. Do not use purchased email lists. These may contain aged, or spam trap inboxes or inboxes that have been filled. In addition, purchased lists are very low quality, increasing the risk that your email will be marked as spam and blacklisted.
  4. Use separate domains or subdomains for marketing, transactional and person-to-person email. This reduces the risk of your business email becoming blacklisted by a bad marketing campaign.
  5. Reduce the frequency of your marketing campaigns. Recipients are more likely to mark email as spam if they feel overwhelmed.

How do you recover your reputation?

If you have landed on Google’s Domain Blocklist, you have a difficult time ahead. All email may be completely refused or immediately sent to the Spam folder. Recovery takes time and patience. If you haven’t already, take the time to go through the steps listed above. Within a few weeks, you should see acceptance rates and open rates improve. If not, you have a more serious issue, Google has permanently blocked your Domain. Your only recourse may be to create a new domain from which to send email.

How does MxToolbox help?

MxToolbox Delivery Center provides the email delivery management and monitoring that you need to keep your messages flowing.

  • Monitor DMARC compliance rates across all senders
  • Closely monitor your Gmail Spam rate.
  • Check your email for 1-Click Unsubscribe, a requirement of Google and Yahoo! bulk sender rules
  • Analyze your campaigns for other potential reasons to miss the inbox with Inbox Placement 
  • Notify you of issues while they’re occurring to enable quick resolution and damage control

If this sounds complicated, MxToolbox also offers Managed Services team that can help you setup DMARC, DKIM, SPF, BIMI and get your domain aligned with Google’s bulk sender policies.

Why Blocklist is really the correct term

For decades, the industry has used the term “blacklist” to refer to IP addresses that have sent spam or domain names included in spammy email, but that’s not really what these lists are. Aside from other issues with the term “Blacklist” (ahem, thank you James Spader) it really is not the most appropriate. Let’s examine the real definitions for email:

Blocklist/Blacklist

A list of IP addresses or domains that should not be trusted because the IP address has sent email to a spam trap, sent email repeatedly marked as spam or may be misconfigured in such a way to encourage spam or other nefarious activity. Domains listed have been included in spam emails or are known to host malware.

Note: MxToolbox is not a blacklist/blocklist. We are not blocking your email, but curate a list of blocklists to provide information about who has listed your IP address or domain as problematic. In some cases, we can help you get delisted, but, in general, you’ll need to work with the blocklist to be removed. There are details on how to be delisted on the Problem Details page for each blocklist. As always, DO NOT PAY to be delisted.

Allow-list/Whitelist

A list of IP addresses that are highly trusted. This is usually used for VPNs, internal traffic, etc. where that IP address should always be allowed.

Note: When dealing with Blocklists, do not ask to be “Whitelisted” as you are not completely trusted. Ask to be “Delisted” and be prepared to prove that you have fixed the issue that caused your IP to be listed.

De-list/Greylist

If you are not 100% trusted, or not mistrusted by being blocklisted, then you are unlisted, or as some would say, “greylisted”. In reality, no company is going to go through the exercise of listing every single IP address that is not Blocklisted or Allowed, so those IP’s are simply unlisted, but still not 100% trusted. Typically, email from an unlisted IP goes through a multi-step process to determine if the email should be allowed in the inbox.

MxToolbox Aids Email Delivery

Focus on the basics of Email Delivery: Technologies like SPF, DKIM and DMARC, and Best Practices in email list management and content relevance. Once your DMARC configuration is really set, then issues like blacklisting are actually more rare and less damaging to your email delivery. Get started today with MxToolbox Delivery Center to get to the Inbox.

Think that you’re on Google’s Blacklist?

Unfortunately, it’s more complicated than that… 

Blacklists have been losing relevance

Blacklists have been a first line of defense against malicious emails since the dawn of the Internet. Every marketer knows that if their sending IP addresses are on a blacklist, their messages are going to be denied. Most email marketers long ago moved to 3rd party senders with large blocks of IP addresses to limit the risk. If legitimate senders can easily change IP addresses, so will spammers, somewhat limiting the long-term value of an IP-based blacklist. Google, Yahoo! and other Inbox Providers know this and have been developing alternative technologies for years.

Blacklists are only the first layer of protection

Blacklists are still relevant for blocking large networks of bad actors and increasing the difficulty of sending spam, however, Inbox Providers like Google and Yahoo! have long taken a layered approach to Inbox Placement. Rather than relying on a simple binary approach with a Blacklist, Inbox Providers use:

  • TLS Encryption for connection
  • Blacklists (both internal and external)
  • DMARC Compliance (SPF Authentication, SPF Alignment, DKIM Alignment)
  • Spam Content Scoring Rules
  • Bulk Sender Spam Reporting Rules
  • Individual Spam/Junk Rules

If you are a legitimate sender of emails, more than likely, you are not on Google’s Blacklist. More likely, your email is being filtered by these other layers of their inbox protection.

Google is making changes to Bulk Sender Rules

Both Google and Yahoo! have announced changes to their Bulk Sender policies for 2024. Bulk Senders are any senders with more than 5000 emails per day. These senders will now be required to:

  • Maintain SPF, DKIM and DMARC Compliance
  • Have a 1-Click unsubscribe link on every email
  • Maintain a rate of messages marked as Spam less than 0.3% (or 1 in 333 message marked as spam

While Google and Yahoo! represent a large portion of hosted Inboxes, other Inbox Providers will keeping a close eye on these changes. Expect similar conditions for accessing Office365/Outlook.com and other major Inbox Providers in the near future. In addition, we expect that Google and Yahoo! may revisit and strengthen the volume and spam rate requirements.

How Can MxToolbox Help?

To maintain access to the Google Inbox, you need tools like MxToolbox Delivery Center. Our suite of email delivery tools helps your sending domain achieve the best possible email delivery rates, including issues with SPF, DKIM and DMARC. More importantly, our Inbox Placement feature will tell you if your campaigns are being sent to the Spam/Junk folders or actually making it to inboxes, as well as which Inbox Provider(s) you are having trouble sending to.

MxToolbox is the Expert on email delivery. We offer a wide range of email delivery services, including a fully managed email delivery service, so be proactive now and take advantage of them before these new 2024 guidelines are applied to your outgoing newsletters and marketing campaigns.

Are Blacklists still relevant?

Blacklists were developed as a way to mark IP addresses used to send spam, IP addresses at risk of sending spam due to poor configuration or domains used in spam emails.  Blacklists would be consulted by an inbox owner when making email delivery decisions and should not be used to modify web traffic.  

The Arms Race

Early on spammers could set up an email server on any network and send unsolicited email to whatever email addresses they could scrape off the Internet.  Inbox Providers and other Companies then set up lists of IP addresses that were sending spam and shared them with each other – the first blocklist/blacklists came from these casually developed lists.  Eventually, blacklist providers emerged as a profitable business model and even developed traps to harvest the IP addresses of spammers without impacting actual users.  Blacklists became highly useful to block malicious email from a single email-sending IP address or small network.

Spammers could see the inevitable downturn in their scams and quickly changed IP addresses to resume sending spam.  Blacklists detected the new spam IP address, listed it and Inbox Providers blocked email from it.  This cycle continued.  Some Blacklists started listing entire networks and Internet Service Providers to stop them facilitating spam.  The downside is that legitimate senders can get caught in this cycle, but often have trouble changing IP addresses.  Delisting is available but sometimes time-consuming which delays or degrades regular business operations.  

Legitimate Email Marketing Can Be Blocked

Email marketing became a necessity to get a business growing on the Internet.  Setting up a mail server, maintaining it and keeping it off of a blacklist with any sort of email volume was difficult for smaller businesses.  Large companies could easily afford a big pool of IP addresses and several mail servers to shift load around. Entrepreneurs stepped in and created email marketing/email blasting companies to fill the gap. Email marketing firms took on the risk of blacklisting and the responsibility of moving the load around, as well as getting the IP addresses delisted in a timely manner.  But, which emailers were legitimate and which were spammers?   SPF, Sender Policy Framework, allowed businesses to designate an email marketing company as a legitimate partner.

New Technologies Emerge

Inbox Providers then changed the game, scanning for SPF to ensure legitimate outsourcing.  Most companies will not process an email if it does not pass SPF Authentication or SPF Alignment.  The next step was checking digital signatures using DKIM and tying it all together with DMARC.  This created a big bar to jump for many spammers, but also businesses.  An email needs to pass SPF or DKIM checks to be DMARC compliant and a sender needs to actively manage email configurations to get an email delivered.  A comprehensive email delivery tool like MxToolbox Delivery Center has become a necessity for understanding DMARC reports, managing configurations and maintaining good email delivery.

Spammers are beginning to adapt by hacking legitimate business email accounts or adopting SPF, DKIM and DMARC for their look-alike spam domains.  Unfortunately, small businesses are still lagging behind and their email delivery is suffering. SPF, DKIM and DMARC have become the minimum for good email delivery,  

So, are Blacklists Still Relevant?

Blacklists are less important than they were in the past.  You should think of email security as layers on an onion:

  • Blacklists
  • SPF
  • DKIM
  • DMARC
  • Internal Filters
  • Relevance Filters

If being on a blacklist is affecting your business, your email isn’t even making the first layer of security and you’ve failed to take advantage of all the tools you have available to manage your email deliverability.  Being blacklisted is like a heart attack, it’s a sign that you need to rethink everything, change your email practices and adapt to the new technology landscape.

Ultimately, blacklists may only be useful for on-premise email hosts and will lose some relevance, especially for Inbox Providers like Google, Yahoo! and Office365. Blacklists are brute-force and can eliminate legitimate, relevant email when blocking spam. There are many more layers to jump through before you get to the Inbox that are easier for Inbox Providers to maintain and more effective at blocking undesired email and passing legitimate useful communications.  All businesses need to adopt the current email best practices: 3rd party email senders, setting up SPF, DKIM, DMARC, leveraging DMARC Reporting, etc.  

How can MxToolbox help?

Get started with Inbox Placement!  Your goal is to get to the Inbox, so start there.  We’ll analyze your email configuration and content to give you clear reasons why your campaigns aren’t making it and make recommendations to help you get there. MxToolbox Delivery Center also provides deep insight into DMARC, SPF and DKIM configurations and allows you to obtain feedback on recipient complaints, DMARC reports and emerging email threats.  Get comprehensive insight into your email delivery with Delivery Center.

Are blacklists legal, ethical, etc?

Blacklists came about as a response to unethical and illegal spam.  Blacklists have no other purpose but to stop bad or malicious acts, so they typically occupy the ethical high ground. Since they are used by businesses, universities and internet service providers to screen traffic, they are incented to be ethical, list only known bad actors and not list legitimate commercial traffic.  To do otherwise would undermine the value of their service to their own customers.

All that said, MxToolbox carefully curates a list of the most used and best maintained blacklists.  All the blacklists we check provide free delisting services.  We feel that requiring payment for delisting is not ethical.  However, a few blacklists offer expedited delisting services, which is a bit of a grey area.  Other blacklists may ask strange or seemingly random questions.  Think of this as geeks being geeks, rather than anything malicious or unethical.

What does being blacklisted mean?

Being on a blacklist is a sign of trouble for your email deliverability.  Since companies screen out traffic from blacklisted IP addresses, your emails may be dumped into a spam folder or refused completely.  If your email server’s IP address is blacklisted, it could make doing business difficult.  It’s also a sign that your servers may have been used for spreading spam, viruses or malware.  This could indicate a security breach or an employee issue.  

If your website IP address is blacklisted, then you have a bigger problem.  Typically, web servers do not send email.  Since the primary means of collecting bad actor IP addresses is via email, your web servers might be sending email without your knowledge.  This is definitely a sign of a malware or virus infection on those servers, or someone running email inappropriately from a web server.  

Occasionally, small businesses will run email and web on the same servers.  If you do, you run the risk of a blacklist event taking out all your e-commerce channels because companies may deny access to your website and email activity based upon your blacklist status.

Domain blacklisting is a serious issue.  It means that someone is using your domain for malicious activity, either on a server hosting your website, or by breaking into your DNS.  If the activity is coming from a server in your datacenter, then you need to root out the virus or malware on your servers, patch your servers, and upgrade your security systems and firewalls.  If the activity is coming from a server outside your datacenter that is using your domain name or a subdomain, you have another big problem.  In this case, your DNS has been hacked and the attackers have added subdomains that use your brand.  The attackers can utilize the remote server to host malware and viruses all the while using your brand to make their attacks look legitimate.

Regardless of the type of blacklist, being blacklisted could be a serious issue.  MxToolbox Monitoring services can help you by letting you know when you have been blacklisted, giving you notice before it becomes a serious business issue.

How do I get delisted?

Each blacklist has it’s own method for delisting.  Sometimes it’s a webform, sometimes it is an email.  Almost always, you need to include the steps you took to fix whatever problem put you on a blacklist.  Many blacklist operators see themselves as righteous crusaders fighting against spam, malware, viruses, bad email configurations and poor email operations, so remember when dealing with a blacklist operator, you are the bad actor seeking forgiveness.

Tips for delisting:

    • Read the description of the blacklist – Descriptions on MxToolbox Blacklist Info Pages give you everything you need to know about the blacklist and your reasons for being listed.  
    • Ask yourself “Do I need to be delisted?” and “Is this affecting my business?” – If you do not do business in Spanish, chance are you don’t need to be removed from the NoSolicitado blacklist that only serves Spanish language emails.  If you aren’t seeing any emails bouncing back, then this isn’t a huge issue, yet.  Don’t waste time or get frustrated over listings that have no effect on business.  
      MxToolbox provides filters that allow you to ignore alerts on irrelevant blacklists.  We also provide an MxReputation report that tells you what your global reputation is.  If it’s still high, you might be fine ignoring this blacklist.
    • Take care of the problem that caused the blacklisting – Once you know why you were listed, fix those issues.  Patch servers, run anti-malware/anti-virus software, fire the guy in marketing that was CCing all your customers or whatever you need to do. A blacklist will not delist you if you have changed nothing.
    • Have a detailed list of remediation steps you have taken –
      What did you do to clean viruses or malware?
      What did you do to close hacked accounts and prevent future attacks?
      Have you changed outbound email policies to prevent spam?
      Have you patched servers or firewalls?
    • Visit their site and fill out the required forms carefully and completely – MxToolbox has links to all the blacklist websites, including delisting forms.  Their forms are for their protection.  Their users will question a delisting if it results in further spam, so filling them out completely will aid your case.
    • Be polite – Most blacklists have evidence that your servers have acted badly.  Treat this as a respectful request that your servers be delisted because you are technically the bad actor here.
    • Explain the business impact – Let them know that you have a business that is impacted by being listed.
    • Be patient, wait a few days for a response – This is not an instantaneous delisting process.  Some of these blacklists are small shops with a handful of employees.  They also need time to validate that you are no longer spamming, sending malware or other issues.  They will wait to see that your emails are no longer hitting their spam traps or being reported by any new customers.  Be patient.
    • Don’t make multiple requests – It’s okay to make a second request if you have heard nothing in a few days, but refrain from making multiple requests in the first few days of an inquiry.  Blacklists get hundreds or thousands of requests daily and often duplicates drop to the bottom.
    • Don’t pay to delist – All the blacklists checked by MxToolbox provide free delisting services.  A few offer paid expedited delisting services.  MxToolbox does not recommend paying to delist and we do not condone services that require payment.  

After you’ve gone through these steps, you should consider setting up monitoring on your important IP addresses, especially Email and Web servers.  Monitors can alert you to blacklist events as they emerge, rather than waiting for serious business impacts.  MxToolbox offers a wide range of monitoring solutions from Free, single IP solutions, to real-time large network blacklist monitoring.

How are blacklists used?

Organizations use blacklists to limit security threats like spam, malware and viruses. The IP address of a server sending email is pulled from the email’s header and compared to the blacklist.  Anything that originates from an IP address on the blacklist is refused, quarantined or dumped to a spam folder.  Similarly, content of an email is scanned against the domain blacklist.  Any emails from or containing a domain on a blacklist will be dealt with.

Some companies also utilize blacklists to scan inbound or outbound web traffic or to create web or email filtering appliances.  Many companies purchase or utilize multiple blacklists along with their own blacklist information to minimize the potential for spam, malware or viruses passing through their servers.

MxToolbox provides insight into the blacklist reputation of your IPs and Domains.

 

What is a Blacklist?

A blacklist is simply a list of IP addresses or domain names that an organization has decided to block for one reason or another.  Blacklists started as a means to combat email spam.    Early on, it was just a list of IP addresses or domain names that were sending junk email.  These lists were manually managed with IPs added and removed based upon human interactions between a few systems administrators.  As the Internet evolved these individual lists became larger, more centralized and list curators developed unique tools, spam traps and service models to make the lists more widely available, and more accurate.

There are a few different types of Blacklists that you need to be aware of to fully understand the market.

Public/Private

Public Blacklists are shared publicly via the web or, more traditionally, via DNS.  A public blacklist can be referenced by anyone online to check individual IP addresses.  Checking more than one list or more than one IP requires development of tools, like MxToolbox that can programmatically check these lists.  Often a subscription to the full list can be purchased for use internally, or commercially in appliances or software. Examples of public blacklist are SORBS and Spamhaus Zen.

Private Blacklists have been setup by a company for their own security usage and are not made available externally.  Often, these are considered proprietary or trade secrets because proprietary methods of data collection are used in the curation of the list.  Examples of these include your ISP’s blacklist, Microsoft’s blacklist and those used by security companies.

IP/Domain

IP Blacklists contain a list of IP addresses that are suspect.  Typically, each IP blacklist has a different method of generating suspect email or web traffic and therefore different reason for listing the IP address.  Typical reasons for listing are:

  • Spam has been received from this IP in a honey trap, directly by the organization or has been reported by subscribers to the list.
  • Malware or viruses were sent from this IP address.
  • Open relays or other configuration issues allow for bad actors to exploit the server at this IP address for spam or malware distribution.
  • This IP address has been marked as dynamic (DHCP) by the owner and leased out to their customers.  Since it is dynamic, no servers should be on these IPs and you cannot trust the ones that are.

Note: If you are on a dynamic IP address, you will automatically be blacklisted by most blacklists.  This is normal.  If you’re not sure if you are on a static IP, then you’re probably not on a static IP.

Domain Blacklists simply list domains that have been found in spam email or are known to be sources of malware infections.  There are only a handful of domain blacklists or blacklists that list domains alongside IP addresses.  While a Domain Blacklist is a useful tool to alert you to reputation issues, they do not contain comprehensive domain reputation information.  In general, checking your website’s IP address against an IP blacklist is also necessary to protect the reputation of your website and checking the IP addresses of your email servers is necessary for protecting your email reputation.

You can find the full list of blacklists checked by MxToolbox here.