What Triggers Email Spam Filters & How Can You Avoid Them?

Why Are Your Emails Going to Spam? & Best Practices To Avoid Email Spam Filters

Despite all of the time and effort you put into curating and delivering the best email campaigns possible, none of it makes a difference if your messages go straight to the spam folder – out of sight and out of mind. Of all of the factors and tools that govern email deliverability, one of the most critical is spam filters. Failure to follow spam guidelines can negatively impact your number of opens, clicks, and – most importantly – sales. Therefore, it is imperative to have a comprehensive understanding of what spam filters are, how they work, and how to consistently bypass them.


What is a Spam Filter?

Spam is defined as unsolicited bulk email (UBE) sent as a mass mailing without the recipients’ permission. Statistics show that approximately 45% of  emails sent each day are classified as spam. That amounts to 14.5 billion spam emails per day. With numbers that high, it makes sense that programs like spam filters were designed to identify spam and block such intrusive messages from making it into inboxes. However, spam filters can negatively impact email marketing performance, forcing marketers to jump over multiple hurdles just to make it into inboxes in the first place.


Why Emails Go to Spam Instead of the Inbox


The Controlling the Assault of Non-Solicited Pornography and Marketing (CAN-SPAM) Act was a critical law passed in 2003 that set new national standards for email. The law instilled requirements for commercial messages, affording recipients the right to cease receiving emails from any company. The following is a breakdown of CAN-SPAM’s main stipulations.
  • Do not use false or misleading header information.
  • Do not use deceptive subject lines.
  • Clearly identify your message as an advertisement.
  • Inform recipients of your location 
  • Educate recipients how to opt out of receiving future emails from you.
  • Honor opt-out requests expeditiously.
  • Monitor what others are doing on your behalf.
Companies that fail to comply with any of these provisions are subject to penalties of up to $42,530 for each and every individual email sent. Needless to say, these figures can add up very quickly. For more information on the CAN-SPAM act, visit the Federal Trade Commission (FTC) website.


Common Reasons Why Emails Go to Spam

You Weren’t Given Permission to Email

You must always receive permission to add someone to your email marketing list. Failure to do so will not only guarantee that your emails end up in the spam folder, it could also lead to greater issues – like legal concerns and substantial fines. In order to ensure that you have the full consent of all recipients, design an opt-in form on your website that explicitly clarifies that your website’s visitors are actually subscribing to an email list. Never, under any circumstances, add emails to your marketing list that have been collected from offline sources, such as business cards or via contacts made at conferences. If you wish to add any of these leads to your list, you are legally obligated to send a personal email requesting permission.

You Have Low Engagement Rates

Nowadays, inbox providers like Gmail, Outlook, and Yahoo utilize a sophisticated set of engagement metrics to determine the likelihood of whether or not users actually want to see your emails. Positive engagement signals include when recipients open your emails, send a reply, and add your contact information to their address books. On the other hand, negative engagement signals include ignoring your messages, transferring them to the junk folder, or deleting them altogether. Make sure you send emails specifically designed to maximize engagement. If you have low engagement rates and are sending negative signals, you are much more likely to wind up in the spam folder.

You Included Attachments in Your Emails

While it is common practice to include attachments in emails to people who are expecting to hear from you, doing so in bulk will trigger spam filters. This is because actual spam emails typically contain harmful attachments. In turn, spam filters are designed to detect and remove emails with attachments. Spam also increases the size of your email – making them longer to load. All the information you need to include should be in the body of the email. If you wish to incorporate any additional material, do so with a link to another page rather than an attachment.

Email Content: Too Many Images & Not Enough Text

Since spam and phishing emails tend to be short, emails with insufficient text are likely to be flagged as spam. However, do not overcompensate and make your messages too long, either. Research data suggests that the optimal email length is between 50 and 125 words. As a rule of thumb, you should always keep your emails under 200 words. Meanwhile, emails that contain mostly images may be considered spam, so only use images that are essential to the email content. A common guideline for text to image ratio is the 60/40 rule, in which your messaging has a minimum of 60 percent text and a maximum of 40 percent imagery. Also, be sure to keep your font size, style, and color consistent.

Your Sender Information is Inaccurate or Misleading

Sender information is the information that appears to subscribers in the following fields of an email:
  • “From”
  • “To”
  • “Reply-to”
You must use accurate sender information in both your email body and sending domain. Whether it is intentional or not, misleading people with inaccurate sender information is illegal. In addition, do not include any numbers, exclamation points, or other eye-grabbing characters as a ploy to get the reader’s attention. At the bottom of each email, include a name that subscribers can easily recognize and trust. This could be the name of a company employee, your company name, or both. Do not use “noreply@yourcompany.com” as your “reply-to” domain. Instead, use an address that people are able to respond to, such as “feedback@yourcompany.com.”

The Email Didn’t Include a Physical Address

The law dictates that you must always include your company’s physical address in your emails. Therefore, always include your current business address, a PO box registered with the national postal service, or a private mailbox.

You Didn’t Include an “Unsubscribe”/”Opt-Out” Link

You are always required to give people a chance to “unsubscribe” or “opt out” from the emails you send. Failure to do so can lead to penalties and fines like those listed in the CAN-SPAM act. In the body of your emails, include elements that comply with unsubscribe link regulations. For instance:
  • Make it as simple and straightforward as possible to unsubscribe. It should be easy for readers to locate the link and follow a 1-click process.
  • Any unsubscribe request must be processed within 10 business days.
  • Only ask for reasons why readers are unsubscribing after they have been removed from the list.
The logic is simple. If readers do not wish to receive emails from you and have no way of opting out, then they are far more likely to report your messages as spam.

Incorrect Spelling and Grammar

Since most junk and phishing emails are poorly written, spam filters analyze emails for spelling and grammar mistakes. Sending an email with typos and grammatical errors will likely send your emails to the spam folder Even if they don’t get flagged by spam filters, sending emails with these errors will not be appreciated by people and are likely to manually report it as spam. Always proofread and double check emails for spelling and grammatical errors before sending.

You Used Spammy/Red Flag Words

Never use spam-centric words in any portion of your emails. There is a firm list of words in either your subject line or body that will trigger spam and be blocked by filters. Here is a list of red flag spam trigger words and terms:

If any of your messaging requires the usage of any of these terms (like when running a promotion) then try to use synonyms of red flag words to communicate your point. If your offer is strong enough on its own, there is no need to be blunt in your wording. Also, refrain from using ALL CAPS or Exclamation points!!!

You’re Emailing Inactive Addresses

Inactive email addresses can belong to individuals who have not engaged with your messaging for an extended period of time. There can be a number of reasons for this. While they could be using their address regularly and simply ignoring your content, the addresses themselves could also not be in use anymore. Be on the lookout for hard bounces, auto responses, or notifications that your messages were either not delivered or the particular address was not found. Spam filters will flag your emails if you are constantly sending emails to inactive addresses. In turn, make sure that you keep your email lists up to date by monitoring and removing any inactive addresses.

How to Prevent Emails From Going to Spam [Best Practices]

Never Buy An Email List: Always Build Your Own

Never buy, rent, share, co-register an email list from a third party, or harvest email addresses online. Not only do these practices constitute a clear invasion of privacy, they directly violate the aforementioned CAN-SPAM Act. Although it will take more time and effort, always build your email list organically using an authentic, foolproof opt-in process. While it may seem appealing to build a list more quickly, it won’t make a difference if you wind up in spam folders, break the law, and become blacklisted.

Use a Reliable Email Service Provider (ESP)

Always use a trustworthy, reputable, reliable ESP, since the IP addresses associated with them are trusted and less likely to be flagged as spam.

Use Segmentation to Send Targeted Emails to Relevant Audiences

Effective segmentation can significantly increase the impact of email marketing campaigns. Therefore, segment your email list to target individual subscribers with content that is highly relevant to them. If you are going to ask a consumer to spend his/her valuable time and money purchasing your product, make sure you are speaking to the right person, at the right time, with the right pitch. The more relevant it is, the less likely people are to either mark it as spam or delete it, and the more likely they are to open your message and positively engage with your brand.

Provide a Double Opt-In & Ask to Be Whitelisted

In order to be safe, Google recommends implementing a double opt-in subscription process to fully ensure that recipients wish to receive messages from your brand. An efficient way to do this is to issue subscribers with a welcome email that they must confirm – either by clicking a link or pressing a button – before they are formally added to your email list. The second opt-in email can also be a way to request subscribers to whitelist you by adding you to their contact list. Being on their approved senders lists gives full assurance that your future emails will never get flagged by spam filters. This is a simple extra step that guarantees your subscribers truly wish to hear from you. It also helps keep your email list clean and relevant – positively impacting both your reputation and standing in the eyes of inbox providers.

Regularly Clean Your Email List

Make it a part of your workflow to consistently audit and update your email list. The more inactive or abandoned addresses you have, the lower your overall delivery/engagement rates will be. This can damage your reputation and increase the odds of being relegated to spam. In turn, if certain subscribers have not engaged with your emails for an extended period of time, consider removing them from your list.

Monitor Your Engagement Metrics & Sender Reputation

Continuously monitor your email campaign engagement and make adjustments as quickly and efficiently as possible. Key metrics to track include open rates, click through rates, delivery errors, and spam complaints. This For instance, a high number of delivery errors is a sign to clean up your email list. Or, if you have low open rates, test out different subject lines until they improve. If the issue persists, consider retooling your strategy altogether. Additionally, persistently monitor your sender reputation to ensure your email servers IP address has not been blacklisted There are multiple tools online that can analyze your IP address and domain to check if you have been blacklisted by any inbox providers. If you have been blacklisted, submit a request as soon as possible to be reinstated. There are also a variety of spam checking tools that can analyze your sending reputation and allocate a score – typically from 0 to 100. The higher the score, the less likely that your emails will be flagged by spam filters. They include:

Send Useful Content

The key driver behind every successful email marketing campaign is the dedication to sending useful, intriguing content to your subscriber base. Never send emails just for the sake of it. If there is no clear intent behind your messages, your engagement will drop and spam rates will climb. No one likes content that is too salesy – particularly if the pitches do not match their personal tastes. Segmenting your list among different groups and life stages allows you to send targeted, personalized, and valuable information to distinct members of your audience.


There are many factors that make up a successful email marketing campaign, and spam filters can have a much larger impact than you think. Simply being aware of the red flags and sticking to best practices detailed above will ensure that you are maximizing your critical engagement metrics while gaining an advantage over your competition. Remember, higher open and click through rates don’t just lead to more sales, they send positive signs to inbox providers that help secure your rightful place in subscribers’ inboxes down the road.