But the truth of the matter is, you’re most likely not even seeing the majority of the spam that is sent to your inbox. 


With over 80% of email content sent being spam, how do you as a marketer ensure your message makes it to the customer? 

That’s thanks to spam filters. Your email provider automatically filters through the emails that are sent to your inbox and sorts those that show signs of spam into a folder you probably never check. Without spam filters, you’d likely have to sort through 20-30 more emails a day. On top of that, you’d have to hope nothing you click on is a scam. 

For us as consumers, this is great. We have less clutter and irrelevant content to consume every day and a protective layer against scammers who may be trying to take advantage of us. But how does this affect email marketing efforts for companies? 

To understand this, we need to first understand why these filters are important and take a look at the types of spam filters and what they do. From there, we can start to make sense of how spam filters can affect marketing efforts, and how you can avoid being routed to a user’s spam folder.

Why Email Spam Filters Matter

This may seem like a no brainer for most of you, but we still feel it is important to take a quick step back and talk about why spam filters matter. 

Spam emails can be harmless promotional content that has a spam trigger word in it. But they can also contain malicious content that is aimed at infecting computers with malware and potentially scamming an unsuspecting user. 

In fact, over 20% of spam emails contain malicious attachments. If you were to receive an email like this and open the attachment, you would put your personal information and documents at risk. Luckily, as mentioned above, our email providers are getting pretty good at filtering these attacks out. 


This chart shows why spam filters are so important. Phishing scams target people with a variety of different tactics and are getting more and more realistic every day. For many people, if these were not sorted out for them, they’d become victim to a scammer.

So, as digital marketers, we need to know what triggers will send an email to a spam folder and how to avoid this at all costs. An email that ends up in a spam folder generally doesn’t get read and is wasted time for us. 

Understanding Email Spam Filters

There are a number of different types of spam filters out there. To make sure that your emails don’t get caught in them, you need to have a basic understanding of each. Although this list does not include every filter option out there, it will give you a few things to consider when developing your next email. 

  • Content spam filters. These types of filters look for certain words or phrases that identify a spam email. Depending on what products or services you are offering, this is something you’ll want to consider when writing copy for emails. 
  • Permission spam filters. Another type of filter that could affect your emails from making it to a user’s inbox. This means that the subscriber has to approve that your emails can make it to their inbox. No approval means automatic filtering to the spam folder. 
  • Blacklist spam filters. Email providers can identify repeat offenders when it comes to spam emails. With a blacklist filter, they can automatically filter out any emails from known spam senders. 
  • Rule-based spam filters. Similar to the content spam filter, rule-based filters can be set up to identify specific wording or content. Whether the email is sent to the user’s inbox or spam folder will depend on content and keywords within the body or header of the email.

While these are some of the most common, there are many other scenarios spam filter options to protect email subscribers from malicious spam filters. We encourage you to take the time to dive deeper into each type of spam filter so that your emails will reach their highest potential. 

But before you go, let’s take a quick look at a few best practices and a real example of how spam filters affect email subscribers. 

Get Your Emails Through Spam Filters

Spam filters are very good at identifying possible threats. But, that also means that marketing emails sometimes get flagged and sent to the spam folder. These filters are getting so good, that only around 85% of marketing emails actually make it to a customer’s inbox. 

So that’s why understanding the different types of spam filters is just the first step. After that, you need to take what you’ve learned and put it into practice. Let’s take a look at a few different best practices when it comes to surviving the email spam filter.

Keep Your Email List Clean

Hopefully, you’re already regularly reviewing your subscriber list. But if you’re not, this is a great place to start. Make sure that you are regularly cleaning and maintaining the contacts on your list. This will help you continue to reach out to the customers who want to hear from you while identifying those with lower engagement and pulling back the communications to them. 

This is important because if you send too many emails that with poor results, your emails are much more likely to be sent to the spam folder. A smaller list that has a higher engagement rate is a better solution than sending a large unengaged list email that they don’t want. 

Also, another note when it comes to email lists, always make sure to build your own lists. Purchasing email lists is often a quick way to get flagged and penalized by email providers. 

Content to Avoid When Writing Emails

The content of an email is a big indicator when it comes to identifying spam. You’ll want to avoid certain words, phrases, and other spam signals. Here’s a quick list of a few different things you’ll want to consider leaving out when writing your marketing emails. 

Avoid using these spam trigger words and phrases: 

  • Bonus
  • Free
  • Cash
  • Order now
  • Lowest price
  • Winner 
  • Risk-free
  • While supplies last

This is only a shortlist of the hundreds of words that can be spam triggers. Make sure you are writing emails and subject lines carefully to avoid getting marked as spam. 

A few other content related tips:

  • Don’t write in all caps
  • Too many exclamation points can seem suspicious 
  • Use $$$ will likely end poorly 

Follow Opt-in and Unsubscribe Protocols

All email marketing must have an option for users to opt-in and easily unsubscribe. This is not just a best practice when it comes to spam filters, but something that is governed in the world of email. But by making sure you are following these regulations will help protect you from spam filters as well. 

If a subscriber tries to unsubscribe, or never opted-in to your emails, they are much more likely to mark your emails as spam. The more times your emails are marked as spam, the more likely spam filters will start to see this and begin filtering your emails to spam folders. Do this too much and you may find yourself on the blacklist -- a place you do not want to be. 

AOL Changes Spam Filtering

To share a real-life example, let’s take a quick look at how AOL changed their spam filter in the past. In XXX AOL announced on their POSTMASTER BLOG that they made changes to their spam filtering.  In a post from Lili Crowley, it was announced that based on customer feedback changes have been made to the handling of identified spam.  As a result, some senders may be blocked with 554 CON:B1 Refuses. AOL’s Postmaster website defines a 554 CON:B1as “The IP address has been blocked due to a spike in unfavorable e-mail statistics”.  

This type of error message would indicate that the sender has been blocked due to a poor sending reputation. Senders found that  even though  they were able to deliver email in the past without any major deliverability issues, they may not be able to be delivered due to this new restriction.

This is an important example to consider because although you may be doing everything you can to avoid being marked as spam, the filters are always changing. You need to stay up-to-date and know what adjustments you need to make as email providers make changes such as this.

Did you know that it’s estimated that over 80% of emails sent are considered spam? That’s an extremely high number when you consider how many emails you receive in a day.