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Understanding Email Spam Fighting Technologies

Email SPAM has become a significant issue for consumers and businesses. At times SPAM can be funny, annoying, and, unfortunately, very dangerous. Over half of the email traffic is SPAM. For April 2020 alone, an analysis from Cisco Talos Intelligence put the average daily spam volume at 320 billion. Google's email service blocks more than 100 million phishing emails every day, and during the pandemic, they said out of those, 18 million were related to COVID-19 in some way. 94% of malware is delivered over email, and one in every 3,000 email messages contain malware payloads. 76% of companies have fallen prey to phishing scams. Every year SPAM costs businesses over $20.5 billion. In a few years, analysts predict it will reach $257 billion annually. Email SPAM is a big problem.

Companies are investing a significant amount of money in fighting email SPAM. The global enterprise SPAM market is growing at such a rapid pace. In 2018 the market was valued at $849 million and will increase in the next several years to $2,675 million at a CAGR of around 17.5%. Significant money is being invested into fighting SPAM, making it very hard for companies to send cold outreach emails. Google's machine learning algorithm that powers the SPAM filter for 1.5 billion Google email users is believed to be 99.5% accurate. As more advanced SPAM technologies are being developed, businesses need to understand these technologies and learn how to play within the rules to ensure their emails get delivered.

SPAM Technologies Protect The Inbox

To solve the massive SPAM problem, mailbox providers ended up inventing SPAM filters, Firewalls, and Blacklist directories. SPAM technologies is software that uses artificial intelligence to decide what emails should exist in your inbox and which ones should go to your spam folder or blocked altogether. Inbox providers are highly incentivized to provide better SPAM technologies. Since 70% of email is SPAM, a good SPAM filtering technology will reduce the number of emails being processed by your inbox and increase the businesses' profit margin. Also, SPAM technologies protect their customers from malware and phishing attacks, which helps drive customer loyalty. In a highly competitive market, like the inbox market, it is essential to maintain a reputable brand to keep your customers from opening another email box with your competitors.

How Spam Technologies Work

To understand SPAM technologies, we must first understand the building block technologies ensuring your emails get delivered. Here are some of the tools you need to know:

Email Service Provider (ESP)- ESP or email marketing software (like Sales Innovator) helps you send emails at scale.

Internet Service Providers (ISP) - ISP stands for Internet Service Provider. When we're talking email marketing, ISP refers to the major email providers: AOL, Hotmail, Outlook, Yahoo, Gmail, Comcast, and so on. Their customers are commonly your email recipients. It's the job of the ISP to protect their customers from receiving unwanted or unsolicited emails.

Spam Filters - Decides whether the email should be present in the inbox, promotions tab, spam folder, or whether it should be blocked altogether.

Internet Protocol Address (IP Address) - This is a unique public address of the server over which your emails go. Your ESP typically maintains your IP Address.

Blacklists - Databases that store IP/Domain spammers. There are a lot of them, and their criteria are specific. Just keep in mind that they mainly refer to your email sending activity: sending frequency, sending volume, bounce rate, spam reports.

Custom Blocking - It is common for ISP's and corporate networks to create their SPAM blocking criteria. ISP uses information from blacklists and content filters in a "weighted" system that gives "spam points" for each offensive piece of the message.

Domain Name System (DNS) - The domain name system connects URLs with their IP address. With DNS, it's possible to type words instead of a string of numbers into a browser, allowing people to search for websites and send emails using familiar names. An email address is matched to a domain name, and the domain is matched to an IP address. The DNS matches the address on the email message to its destination and delivers the email. The DNS can access the public key to decode your DKIM and publish the SPF record to authenticate your email.

Now that we are clear with our definitions, you can better understand how these technologies work together. Business senders use email service providers to send emails via ISP's. ISP's use SPF,DKIM, DMARC, and MX Records to verify the sender and recipient's identity. Once a connection is made SPAM technologies help determine if emails should be blocked, added to the SPAM folder, put in the inbox, or filtered to another destination. SPAM technologies use customized technologies such as SPAM

filters and blacklists to decide where the emails should go.

For the rest of this article, we will further describe how SPAM technologies work and how you can learn how to play safe and maintain a high email deliverability level.

Types of SPAM Filters

There are broadly three types of SPAM filters that you will encounter:

Gateway SPAM Filters: A gateway spam filter is an on-premise software solution for filtering spam. This software is installed as a virtual appliance behind the network firewall. Gateway SPAM filters are the first line of defense against spam. Companies providing this solution include Cisco's IronPort and Barracuda.

Hosted SPAM Filters - These types of SPAM filters are cloud-based solutions. Instead of supporting one company, these solutions support various companies and access a lot more data, giving them a more sophisticated SPAM filter. Hosted SPAM filters deliver messages to an inbox, move messages to spam, quarantine messages, and block messages. Two of the leading solutions in this space include Cloudmark & MessageLabs.

Desktop SPAM Filters - These are third-party SPAM filters that exist in a user's system. Desktop spam filters are highly customizable and are more personalized to a specific user. Outlook uses Microsoft's SmartScreen anti-spam filter to filter email.

Major Factors Influencing Spam Filters

Whatever type of SPAM filter your inbox provider users three major factors will impact their decision to filter your message:

  1. Email Reputation - Email, sender, or domain reputation is the measurement of your email's sending practices and how closely you abide by the standards set by your Internet Service provider (ISP). ISP's use different criteria to filter spam and unwanted email. Your email reputation is primarily measured for a sending IP address. Your email reputation is comparable to your credit score. It takes time to build up a good credit score, but it is easy to destroy it if you are not careful.

  2. Email Authentication - Email authentication is a technical solution that certifies your email as a valid email. It affirms that your email comes from who registered your email. Email authentication is used to block harmful or fraudulent uses of email, such as phishing and spam. The most common types of email certifications include SPF, DKIM, and DMARC.

  3. Email Content - Email content is the analysis of your email content and how it follows the guidelines set by your ISP. Email filers tool for emails containing "spammy" language, too many uses of images, broken HTML, attachments, proper use of hyperlinks, and many other variables that signal SPAM. Most importantly, if email content is low-quality, your users will not engage, and your reputation will be affected.

How GMAIL's SPAM Filter Works

Google's SPAM filter is most likely one of the most advanced SPAM filters. Each day over 1.5 billion people use Gmail, and over 5 million businesses pay Google to use Gmail as part of G Suite. Gmail is the second-largest email client (38%), next to Apple Mail (40%). G Suite is the leading office suite provider with a 58% market share vs. Office 365's 40.93% market share. With a commanding market share, Google's SPAM filter claims to have a 99% accuracy.


Gmail looks at both the domain and IP address of senders when determining where to place an email. Setting up proper authentication for your outgoing email is very important for your email to get accepted and not filtered or blocked by Gmail. Ensure you properly authenticate yourself with your ISP and setup your SPF, DKIM, and DMARC.

User Engagement

User engagement is vital to Gmail's algorithm for determining what should be filtered or blocked. Gmail looks at each person's action in their inbox when deciding what should be filtered. What could be SPAM for one person could be a valuable email for another person, so personalizing filtering is important to Gmail. Here are some examples of the user actions Gmail algorithms take into account when filtering:

  • Messages deleted before being read.

  • Messages marked as SPAM

  • Emails voted as not SPAM

  • Messages moved to the promotions folder

  • Starred messages

  • Messages read

  • Messages replied to

  • SPAM reports or complaints

Because Google highly values engagement, companies need to clean up their subscriber lists and remove subscribers with minimal engagement. Emailing those users will bring down your overall reputation and will send more of your emails to SPAM. Keep the same email cadence with your active users and choose an alternative strategy for your passive subscribers. By segmenting your emails by engagement, you will maintain a good reputation with Google for your engaged subscribers while using an alternative email address and domain for your riskier subscribers.


Content is another factor Gmail analyzes when deciding what content should be blocked or sent to SPAM. Gmail will analyze your email's header, body, images, and links to determine where they should send your email. Avoid "spammy" words is important, but it is not as crucial as a sender's reputation. Gmail highly ranks a sender's reputation as a critical factor in ensuring your emails reach the inbox.

Sending History

If you are using a dedicated IP and have a new IP address, you should warm up your email. Instead of sending a lot of emails right away, you should slowly scale your sending. Gmail blocks new IP addresses for the first 2-24 hours, and after that, it starts delivering a few emails into the inbox and sends some to spam to test recipients' reactions.

If their initial test results in high complaints, then your emails will most likely all land in SPAM. On the other hand, if your emails receive a high engagement rate, you will most likely end up in the inbox. Your first set of emails is critical to determining your future relationship with Gmail.

If you were not successful passing Gmail's test and need to be rescued, your recipients will need to go to their spam folder and mark your emails as "This is not spam". After you receive several of these, your email will be marked safe for the inbox.

Monitoring Your GMAIL Reputation

Gmail provides a tool, "Postmaster Tool" to give you visibility into your current domain reputation, IP reputation, spam complaint rate, and other deliverability statistics. Use this tool to monitor your reputation with Gmail continuously to ensure deliverability.

How Outlooks SPAM Filter Works

Microsoft is the oldest webmail provider, having launched in 1996 and then rebranding to Currently, Outlook has over 400,000 active users. Microsoft also supports businesses with its Microsoft Exchange and Office 365 email and office products, which control 87.5% of the email and authoring market.

Microsoft SPAM filters look at engagement, complaints, spam traps, and other factors similar to other service providers. Although, unlike their competition, they use the Microsoft Sender Reputation Data Network to decide what emails are spam.

Microsoft Sender Reputation Data Network (SRD)

The SRP or SPAM fighters program uses a panel of voters selected randomly from active outlook users to help train their filters. These voters are asked to vote whether the original email was "Junk" or "Not Junk". The votes decide your fate on having your emails sent to SPAM or not. The spam fighter program has been more reliable at finding spam instead of just monitoring complaint rates. Complain rates are a lot easier to manipulate since senders can increase their email volume to reduce the total percentage of complaints.

Monitoring Your Outlook Reputation

Microsoft provides several tools to help you manage your reputation.

Microsoft's Smart Network Data Service (SNDS) - For those using a dedicated IP address, senders can use SNDS to see data about subscriber complaints, email volume, spam trap hits, etc.

Junk Email Reporting Program (JMPR) - Microsoft's feedback loop service sends you a copy of the messages people marked as SPAM. If you are abiding by all best practices and still encountering issues, you can directly submit support tickets to Microsoft.

How Yahoo's SPAM Filter Works

Yahoo still commands 5% of the hosted email market share and Yahoo Business Email is leading in Russia, Belarus, Kazakhstan, Uzbekistan, Poland, and several other eastern European countries. Yahoo utilizes many of the same best practices as Google and Microsoft and specifically calls out the following factors to ensure deliverability:

  • IP address reputation

  • URL reputation

  • Domain reputation

  • Sender reputation

  • Autonomous System Number (ASN) reputation

  • DomainKeys Identification Mail (DKIM) signatures

  • Domain-based Message Authentication Reporting and Conformance (DMARC) authentication

Keeping Email Volume Constant

Yahoo provides many standard recommendations to ensure email deliverability, but they recommend keeping email volume constant. "If you send emails at a certain rate and suddenly have a spike of activity, you could get flagged as a compromised sender and marked as spam. Instead, plan your campaign and spread it out over a period of time."

Yahoo also recommends publishing a reverse DNR record if you have a dedicated sending IP. "Not having a reverse DNS entry can cause your mailing IP to look like a dynamically assigned IP instead of a static mail server."

SPAM Traps Identifying Spammers

Spam traps, also called honeypots, are used to identify and monitor spam emails proactively. Anti-spam organizations, Internet Service Providers (ISPs), and corporations create spam traps to lure spammers. Once spammers are identified through these traps, their IP address or even domain can be denied, affecting your reputation and email deliverability.

You may not be a spammer, but it is essential to know what is a spam trap is and what may cause you to fall into these traps. The last thing you need is to get added to a SPAM trap list and get blocked.

Types of SPAM Traps

Pristine SPAM Trap - This is the most dangerous type of SPAM trap. Other spam traps can negatively affect your reputation, but Pristine traps will most likely get you banned if you get caught, and if you get caught, your IP and Domain will most likely get denied.

ISPs and other organizations set up Pristine spam traps. These organizations create email addresses that have never been previously used by a sender and insert them into websites. Once spammers scrape websites to grow their contact list, the spam traps end up in their email lists. You can also find Pristine SPAM traps in purchased or rented lists.

If an ISP sees someone sending an email on the Pristine spam trap list, you will surely count on your email delivery rate taking a significant dive, or emails will cease to be accepted.

Recycled SPAM Trap - Recycled spam traps are domain registrations or email addresses that were once valid but have been reassigned to be a trap. Examples of this common are sales@, info@, support@, or email addresses of employees who are no longer with the company.

Getting caught sending a recycled SPAM trap email address is not as harmful as a Pristine trap, but it will still affect your reputation.

Email With Typos Trap - The third type of trap is to have domain typos such as "gnail" instead of "gmail" and "yaho" instead of "yahoo" added as spam traps to email lists that people purchase. At times this trap could be an unintentional mistake of a person signing up, but it can still lead to a spam trap.

Domain Spam Traps - Th fourth and lesser-known spam trap is the Domain spam trap. In this case, all email addresses for a particular domain will be a spam trap. Blacklist providers request owners of a dormant domain to point their MX records to the blacklist provider. Then all the emails to that domain become spam traps.

The consequence of getting caught with email typos shows how the sender is negligent and is not regularly cleaning up their contact list and therefore harming their reputation.

How To Protect Yourself From SPAM Traps

There are several things you can do to protect yourself from falling into SPAM traps. Usually, you can prevent them by maintaining a healthy contact list and following email best practices. Here are some other things you can do:

  1. Avoid Purchasing Lists - Using a purchased list almost guarantees that you will run into spam traps. You are playing Russian roulette with every purchased list you use. People on these lists are also likely to mark you as SPAM or delete your emails since they do not know you. All of these actions will negatively affect your reputation and can get you blocked.

  2. List Contamination - Email list contamination occurs when email typos happen in your email list. Email typos could occur accidentally through a data entry mistake or if a prospect entered a correct email address into a form. The best way to protect yourself from list contamination is to double-check your list's emails, verify that they are legit before sending, and enforce a double opt-in for all of your subscribers. Also, note that even if your recipient double opts-in, they can still become inactive later, and their email may be converted to a spam trap. Therefore, continually stay on top of cleaning up your list and not think that double opt-in comprehensively prevent spam traps.

  3. Outdated Emails - Each year, between 15% and 20% of employees turn-over, so your email lists quickly become obsolete. If you are not carefully validating and cleaning your lists, you will fall prey to spam traps. Make sure to always clean-up your email lists and keep those contacts who engage with your emails and remove subscribers that do not respond; this will help you weed out any contacts that could be spam traps.

  4. Pay Attention To Open Rates - Open rates are one of the most critical email metrics. Open rates tell us how the content is doing and what we need to adjust. Also, open rates are a good indication of the potential presence of spam traps in your database. If your subscriber has not engaged with your email in more than six months, then try a re-engagement campaign first. This way, you can find out if they want to remain on your email list. If the email bounces, you should remove the email right away - some may be spam traps. If the email does not bounce and it is not opened, then remove the email. Keeping people on your email list that are not engaged will affect your reputation, so remove them.

  5. Pay Attention To Your Sender Reputation - Your sender reputation can tell you if your emails are hitting any spam traps. Email providers take a lot of metrics into consideration to determine your sender's reputation. Those metrics include spam complaints, sending to unknown users, potential presence in industry blacklists, and more. Although your sender's reputation is critical, they do not paint the complete picture.

How To Know If There Is A SPAM Trap In Your List?

Several indicators can let you know if you have a spam trap in your email list:

Make sure to monitor your delivery rates, and if you see a steady or rapid decline pattern, you may have a spam trap in your email list.

Check to see if your IP address or domain has been listed denied; you likely have a spam trap email in your list. To check if your IP or domain is in any of these popular lists, you can check the following websites:

Barracuda Reputation Block List: BRBL is a DNS blacklist (DNSBL) of IP addresses known to send spam. You can check for free and without signing in to see if your domain is on a blacklist monitored by BRBL.

Invaluement: The Invaluement anti-spam DNSBL blocks elusive types of spam where the sender is sending unsolicited bulk email and escaping traditional detection methods. Several companies use Invaluement to help identify SPAM. They provide a free service to check if your domain has been delisted.

MXToolBox: MXToolbox shows you whether your domain or IP address is blacklisted and can perform checks on your DNS to see how configured. MXToolbox provides a free service but also has more advanced paid features.

MultiRBL: This free multiple DNS blacklist service cross-references other blacklists by IPV4, IPV6, or by domain. They provide a very easy to use interface that gives you a comprehensive view of whether your domain is listed in any blacklists.

Spamcop: The SpamCop Blocking List (SCBL) lists IP addresses that had mail reported as spam by SpamCop users.

Spamhaus: The Spamhaus Project maintains a number of DNSBLs as part of its effort to identify and track spam sources and provide anti-spam protection. You can enter your IP address and domain, and they will check your status for free.

SURBL: Unlike most lists, SURBLs are not lists of message senders. SURBLs are lists of websites that have appeared in unsolicited messages.

Purchase Email Monitoring Tools - You can purchase email monitoring tools that help you stay up-to-date on your campaign performance and if you are running into any issues. Everest is in development and is a good example of such a tool.

How Do I Remove A Spam Trap

The best way to remove space traps on your list is to go through a thorough cleaning of your list. Remove contacts who have not engaged with your list for six months. If this still does not work, then remove those that have not engaged within the last three months.

If you are still having troubles, start to segment your list into segments that you know for sure are not spam traps and those that may be. Continue to narrow your segments until you can locate the spam trap.

You can also hire a consultant to help remove spam traps. They will perform a detailed list segmentation, email validation, and manual curation to identify spam trap emails.

Staying Safe From Filters And Traps

Today there are many innovative technologies and strategies companies are deploying to detect SPAM. SPAM is a billion-dollar problem for companies, and we will for sure encounter more Artificial Intelligence being used to prevent SPAM. As a sender, you need to remember to not act like a spammer and act like a human. This means:

  1. Maintain an outstanding domain and IP reputation.

  2. Make sure your domain and IP are authenticated and certified.

  3. Create great personalized content for your recipients.

  4. Do not purchase email lists.

  5. Regularly scrub your lists of typos and outdated emails.

  6. Use double opt-in to confirm that your recipients are legitimate senders.

  7. Monitor your email delivery rates and your domain and IP reputation.

If you can maintain a healthy contact list and following email sending best practices, you will stay safe from spam filters and traps. In the following chapters, we will deep dive into the best ways you can apply to maximize email deliverability.


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