Author: Dimitar Poydovski

Despite your best efforts as an email marketer, like strict adherence to all general anti-spam policies, you may still find out that some of your recipients don’t receive your emails. Although there is no way to secure 100% email deliverability, you should consider the different reasons why your emails do not reach the subscribers’ inboxes and one of the biggest reasons is that they get flagged as spam. 

Although it may seem intimidating at first, overcoming spam filters and other related delivery issues is not rocket science. With the right knowledge, you can trim down the chances of your emails getting trapped by spam filters and achieve better delivery rates.

Here, we’ll demystify how spam filters work and how they evaluate whether an email is spam or not. We’ll also explore the most critical factors that spam filtering algorithms take into account. Finally, we’ll unravel the 10 most effective tips to make your emails pass even the most strict spam filters. 

So, let’s roll up our sleeves and get your email deliverability soaring.

Why Emails End Up In SPAM?

Let’s face it – everyone has fallen victim to unsolicited and spam emails and wondered how to get rid of them. At best, they are simply annoying but harmless, littering your inbox with irrelevant ads and promotions. However, at their worst, they can cause serious harm, leading to substantial financial and reputational losses. Through spam emails, bad actors conduct social engineering, spoofing, data theft and create all other kinds of trouble. 

To protect their clients from such malicious events, Internet service providers and Email service providers incorporate spam protection systems and spam filters to keep recipients and their networks spam-free. They act as gatekeepers to the recipient’s inbox, putting incoming emails through rigorous and thorough checks before being given a pass. From the moment you send your email till it actually reaches the recipient, it passes through one or more filters aiming to identify and stop malicious or unwanted messages. Every spam filter has its own set of rules, threshold, sensitivity, spam trigger words, etc. You can’t anticipate and predict all, but at least you can understand the most common reasons that trigger spam filters and minimize the chances of your emails ending up in spam folders.   

How Spam Filters Work?

Spam filters use a complex set of rules, algorithms, and AI to evaluate emails and set spam score thresholds. They put every incoming email message under the microscope to decide its fate. After the filters have gone through all checks, they assign a spam score to the emails. If the emails meet the predefined threshold, they are given a safe passage to the recipient’s inbox. However, if the score is higher, they might get expelled to the spam folder; get completely rejected at the network level without any feedback to the sending server; or get directly dropped with an error, something like a hard bounce.

Types of Spam Filters

In general, there are several different types of spam filters, which have a different approach to how they catch spam.

Blacklists

These filters monitor different Denylist/Blacklist databases globally and will stop emails coming from IPs listed in such blacklists. Denylists (blacklists) are databases containing lists of domains and server addresses that have been reported as regular senders of spam content. 

Content Filters

Content filters go through the email message and look for specific words and language that could suggest that the email is clickbait, phishing, or other types of spam. Most content filters look for similar things – bad words used multiple times, such as “offers,” “limited-time,” sexual language, and others. They also watch out for common scams such as the “ 419 scam”, best known when impersonated by a Nigerian prince asking for money against the promise to return a larger sum in the future.

Header Filters

These filters are focused on reading the information transmitted via the header of the email, such as the source IP, if the email is sent to a group of recipients, and more, and aim to ban messages from bad sources, such as IPs known to be used by spammers.

Language Filters

Some Email service providers monitor the language of the emails, and if that language varies from the country language of the recipient, they might stop the messages. These filters may be set differently, but in general, they aim to protect recipients from content that is not tailored to their needs.

Rule-based Filters

Email service providers and users alone can use a filter to set up specific rules that can be applied to all emails coming in. For example, you can set the filter to stop all emails from one specific sender or look for specific words or phrases in the body or in the header of the incoming emails, and if such are detected, the message gets sent to the spam folder.

Bayesian Filter

The Bayesian filters monitor the recipients’ preferences by examining the emails that they send to spam and set rules based on the patterns they detect to automatically flag similar emails in the future. 

AI Filters

AI is being increasingly used to fight spam. Its purpose is to detect patterns in emails, sender behavior, and other suspicious content to help spam filters flag more accurately the messages that go through the network. AI gets trained on the actual incoming and outgoing content of the network, using real messages to learn what is good and what is bad, and its contribution to this fight is getting more and more valuable.

How Spam Filters Calculate the Spam Score?

The Email Service providers constantly update the rules their spam filters use in response to the ever-changing and inventive ways spammers find to catch email users off guard. But even so, there are a few essentials and common criteria that all spam filters consider when forming the spam score of your emails.

Sender Reputation 

The first thing spam filters do, no matter what, is check the sender’s reputation. As discussed in detail in our article on Email deliverability, this refers to the credibility of your sender IP.  If your IP is listed in any Denylists/Blacklists, your emails will be flagged as spam.

Domain Reputation 

Let’s assume your IP is clean, but your domain has a bad history and is known to be sending spam. Again, this information may be recorded in public denylists or private databases of the recipient’s email provider. Unlike the sender reputation, where responsibility is shared with your ESP, the domain reputation is something that you are personally responsible for, and you should monitor it with care.

Email Content Quality

Email content quality is fundamental for both user engagement and spam filter avoidance. High-quality content is relevant, well-written, and provides value to the recipient. When creating email campaigns, email marketers should learn to avoid “spam trigger words” –  specific words or phrases that can activate spam filters. You don’t have to overthink it, but as a rule of thumb, these words are often associated with deceptive or aggressive marketing practices. Remember the Nigerian prince and the content filters above? Just like those.

The quality of the served content heavily impacts user engagement with your emails. High user engagement is a positive signal to email providers that recipients value your content and that you are not sending spam. And vice versa. You can easily monitor that engagement with several metrics – open rates, click rates, replies, and forwards and aim to improve the quality of your emails with every campaign. 

Unengaged subscribers tend to ignore your emails. Like a one-sided conversation, you will have a silent partner who will have no reaction to what you are saying. If your emails are consistently unopened, it signals that your content might not be relevant or desired, and as a result, your future emails are more likely to be directed straight to spam.

What is worse, some of the recipients who open the emails but are not interested in your content might launch spam complaints. With so many scammers online, users have become sensitive to what’s landing in their inboxes, even when they have given consent to receive emails from a certain sender. If you don’t follow strict sending patterns and maintain pristine content quality, they might complain against you and flag your emails as spam.  A spam complaint is a significant blow to your sender reputation. Here are some common triggers that might irritate recipients and lead to spam complaints, which you may want to consider:

• Unexpected Frequency – Sending emails too often or at irregular intervals can frustrate subscribers. 
• Irrelevant Content – Content that doesn’t relate to subscribers’ interests or needs can lead to disengagement.
• Misleading Subject Lines – Crafting misleading subject lines that don’t align with the email body is usually frowned upon.
• Lack of Personalization – Generic, “one-size-fits-all” messages can make subscribers feel undervalued and disengaged.
• Difficult Unsubscription Process – Making it hard to unsubscribe can push users to report your emails as spam instead.

You may also want to consider that the industry-acceptable standard spam complaint rate is less than 0.1% (1 complaint for every 1,000 messages sent). These kinds of rates are not set in stone, but they are set by major email providers like Google and are a good indicator for marketers what to expect if they go above that. Google, AOL, Yahoo, and others give you the opportunity to monitor the complaint rate through their platforms via unique interfaces, which you may want to check out if you wish to keep track and be a better sender.

Now that we have analyzed how spam filters work and what triggers them, let’s get practical and go over the top 10 tips to avoid your emails going to spam.

10 Tips To Avoid The Spam Folder

Let’s dive into 10 of the most practical strategies to keep your emails landing right where you want them – in your subscribers’ inboxes.

1. Build Your Own Email List

The cornerstone of any successful email marketing campaign is a solid, organically grown email list. Refrain from taking shortcuts like buying lists or scraping emails. It can damage your sender reputation and violate privacy laws. Build your list the right way, with people who genuinely want to hear from you.

Do not ever buy email lists or scrape emails! One of the biggest risks, besides the obvious low engagement rate of such contacts, is that you might fall into honeypots. Honeypots are spam trap email addresses used by organizations to catch spammers. They are inactive email addresses solely existing to lure unsuspecting spammers who send unsolicited marketing emails. If you have such an address in your list, it can lead to serious deliverability issues for your campaigns in general.

Craft a blueprint for your list-building strategy that focuses on attracting subscribers through valuable content, engaging social media campaigns, and enticing lead magnets. Make it easy and rewarding for people to sign up, and watch your list grow with interested, engaged subscribers.

SiteGround Email Marketing service comes with a free WordPress Email Marketing plugin that allows you to create signup forms on your website and WooCommerce checkout for collecting leads. That is the first step towards successful email list building since it opens the funnel for all those subscribers to start enrolling.

Once you have a signup form, you may want to revise its positioning – by strategically placing sign-up forms on your web pages and giving them visibility in high-traffic areas, you ensure that more people will engage with them.

And ultimately, you should consider the “incentive” you give your users to subscribe. It may be access to a discount, free content, or else. We have a great article on how to build an email list if you wish to dive deep into the topic.

2. Use Double Opt-In Signup Forms

Forms that require “double opt-in” ensure that only those who truly want to engage with your brand make it onto your list. It’s a two-step process where users confirm their subscription, typically by clicking a link sent to their email. This extra step reduces the likelihood of spam complaints and improves the overall health of your email list.

Implementing double opt-in might seem like a hurdle, but it’s actually an advantage. It seeds out people who accidentally signed up for your newsletter and are unaware of it. They might be unpleasantly surprised when they start receiving your campaigns and act on impulse. There is a high probability that they could report you as spam and damage your reputation. 

The double opt-in helps you verify the subscriber’s interest and email address validity, leading to a more engaged audience and better deliverability. 

3. Authenticate Your Domain

Authenticating your sender domain is a way to prove your emails come from you and not a spammer who hijacked your domain. By verifying your email domain with DNS records, you ensure the recipients’ email servers that the emails come from a legitimate sender. Protocols like Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting & Conformance (DMARC) give your emails safe passage from sender to recipient servers.

Each protocol plays a unique role. SPF prevents email spoofing by verifying sender IP addresses. DKIM adds a digital signature to your emails, ensuring they haven’t been tampered with. DMARC ties the two together, telling receiving servers what to do if an email doesn’t have SPF or DKIM records set. All three mechanisms combined form a strong shield against forging your domain, which instills trust into recipient mail servers and increases your sender reputation. 

If you use SiteGround Email Marketing service to send your emails and your DNS is managed by SiteGround, we automatically set the DKIM and SPF records for you, validating the authenticity of your email campaigns. Here, you can read more about domain authentication in general and specifically on the SiteGround platform.

4. Include Unsubscribe Option in your emails

Always leave the choice for your users to unsubscribe –  not only is it a mandatory requirement in many anti-spam laws, but it also helps you maintain a strong core of an engaged audience. This feature gives the opportunity to users who do not like your content or are not interested to leave your list without harming your reputation. Without an unsubscribe link, these users would just click “report spam” and hit you really hard.

SiteGround Email Marketing users shouldn’t worry about unsubscribe options. All emails sent through our platform contain an Unsubscribe link in the footer by default, and recently, we added an automatic 1-click unsubscribe feature in the email headers to comply with the latest email providers’ requirements.

5. Clean Your Email List Regularly

Regularly removing inactive and unengaged subscribers from your list is fundamental to keeping high email deliverability and improving engagement rates.

Make it a habit to review your list periodically. Remove subscribers who haven’t engaged with your emails over a set period of time. Consider a re-engagement campaign before you hit delete, but if they still don’t give in, it’s time to let them go.

6. Monitor Denylists

Ending up on a denylist can be disastrous for your sender and domain reputation. Avoiding that requires a proactive approach to monitoring your reputation.

You can regularly check if your sender IP or domain is on a denylist using online tools. If you find yourself listed, take immediate action to remedy the situation by reaching out to the denylist operator and rectifying any issues that led to your listing.

If you are using an email service provider to send your campaigns and you notice that your IP is on a blacklist, you should contact that ESP for assistance. 

One such tool to monitor your reputation is MXToolBox, which can provide insights into how your IP address and domain fares in some of the most authoritative denylists. 

7. Be Compliant with Internet Privacy Laws

Internet privacy laws like the CAN-SPAM Act, CASL, GDPR, and CCPA are not just guidelines; they are mandatory for any serious email marketer. Compliance ensures your emails are not only legal but also more likely to be welcomed by recipients.

Understand the requirements of each law, such as providing a clear opt-out mechanism, including your physical mailing address, refraining from using misleading subject lines, and obtaining explicit consent before sending emails. Staying informed and compliant keeps you out of legal trouble and builds trust with your audience.

8. Avoid Spam Triggers 

When crafting your emails, think of spam triggers as landmines on the path to a recipient inbox.  These triggers are specific words, phrases, formatting choices, and even punctuation that can raise red flags for spam filters. Steering clear of these can significantly improve your chances of avoiding the dreaded spam folder.

Spam triggers can be sneaky, often hiding in plain sight within your email content. They range from overly salesy language to aggressive calls to action and even certain words associated with spammy behavior (like “free,” “guarantee,” or “no risk”). Common spam triggers are: 

• Words and phrases suggesting large financial benefits – free money, save big, risk-free, no fees, financial freedom, etc. 
• Phrases and words prompting urgency and immediate actions – urgent, act now, last chance, once in a lifetime, instant, etc. 
• Words and phrases promising on medical cures, health benefits, and sexual stimulants –  cure, miracle, life-changing, lose weight, baldness, cure-all, etc.
• Overly persistent calls to action – get it now, do it today, join millions, start now, etc.
• Excessive use of text in CAPS
• Words and phrases associated with cheap marketing tricks – buy direct, special promotion, increase sales, great offer, you have won, bargain, best prices, etc.

Here is a small list with spam trigger words you must use cautiously:

• Free
• Guarantee
• No risk
• Winner
• Unlimited
• Discount
• Act now
• Offer expires
• Urgent
• Congratulations
• Miracle
• Incredible deal
• Special promotion
• Risk-free
• Prize
• All natural
• Easy money
• Get paid
• Eliminate debt
• Extra cash
• Lowest price
• Winner
• Buy direct
• Cancel at any time
• Cheap
• Save big
• Exclusive deal
• Hidden charges
• Great offer
• No obligation

Another thing to moderate in your email content is images. If you add too many or slow-loading images, this may trigger the spam watchers. Keep it at around 1-2 well-optimized images (using a web tool like TinyPNG) to pass successfully through the spam checkers. 

The key is to communicate your message effectively without setting off alarms. Of course, some of those words will show up in your message, but having too many of those in combination and as a percentage of the overall text is what makes it shady and a spam trigger. Here are some tips on how to steer away from spam triggers: 

• Use Natural Language –  Write as if you’re speaking to a friend. Avoid excessive use of text in capital letters, bold text, and exclamation points, as these can appear shouty and spam-like.
• Be Mindful of Subject Lines – Your subject line is the first thing a recipient sees. Make it engaging but never misleading or “too-good-to-be-true.”
• Balance Text and Images – Emails that are heavy on images with little text can be a red flag. Aim for a healthy balance that’s visually appealing yet informative.
• Keep It Clean –  A cluttered layout with multiple fonts, colors, links and images can not only look spammy but may also confuse your readers. A clean, simple design is more effective and less likely to trigger filters.
• Avoid Deceptive Tactics –  Never try to trick spam filters by using tactics like inserting dots in words (e.g., f.r.e.e). Not only do modern filters see through them, but they also damage your credibility with subscribers.

The definition of what constitutes a spam trigger can evolve as email clients update their filtering algorithms. It’s essential to stay on top of these changes by regularly testing your emails and tweaking content as necessary. A/B testing different elements of your emails can also provide insights into what resonates best with your audience without setting off spam filters.

If you are using SiteGround Email Marketing, you can test your email campaigns by sending them to your own address to catch any spam triggers in advance.  

9. Monitor Your Email Engagement Metrics

Data is your best friend when it comes to avoiding spam. Sadly, there is no way for you to know the exact percentage of the emails you send that get flagged as spam by spam filters. Depending on the reason why your emails get flagged, as well as on the specific filter settings and what they are instructed to do, different things may happen to a “spam” email. They may be rejected by the recipient server at a network level, which means they would never be delivered and reach the spam folder. What is more, recipient servers do not like to communicate specifics on how they handle various types of situations in order to not facilitate spammers into cutting corners. Since often there is no real feedback loop, the sending server cannot gather actual statistics on how many of your emails ended up in spam. 

As the second best alternative, you may want to keep a close eye on metrics measuring email deliverability and user engagement in general. They will provide insights into how your audience and email filters respond to your content: 

• Reported as spam rate –  The percentage of recipients who mark an email from a campaign as spam or junk. This metric indicates how many subscribers consider the emails unwanted or irrelevant enough to report them to their email service provider as spam. It is also your only real “spam” metric, but it does not include data on the emails that ended up in spam folders or got rejected at the network level by filters, which makes this metric alone insufficient.
• Open rate – Measures the percentage of email recipients who open a given email out of the total number of emails sent. Too many unopened emails as a percentage of the total not only indicate a problem with your subject line but also put you at risk of your future emails being flagged as spam.
• Delivery rate –  Indicates the percentage of emails that were successfully delivered to the recipients’ mailboxes (inbox and spam folder including) out of the total number of emails sent in a campaign. The delivery rate focuses on the reachability of the emails. It only measures what part of the sent emails have reached their recipients but doesn’t tell you where they landed or what happens to those that didn’t hit the target. Still, if you have too many undelivered emails there might be different reasons, one of which being a high spam rate.
• Click rate –  Measures the percentage of email recipients who clicked on one or more links within an email. This metric is crucial for gauging the level of engagement and interest your content generates among your audience. It can provide insights into how effective your email content, calls to action, and overall design are at prompting recipients to take the desired action. If your content does not manage to engage subscribers systematically, a chain reaction may follow of declining open rates, unsubscriptions from your email list and increased spam complaints.
• Unsubscribe rate –  Tracks the percentage of recipients who opt out of a mailing list after receiving an email campaign. It is an indicator of how well the content aligns with the audience’s interests and whether the email campaigns meet their expectations. Obviously, it does not indicate any spam risk on its own, but if you notice your unsubscribe rate is high or growing, you may assume that your spam complaint rate might be increasing as well since that shows recipients are getting impatient with your content and will start punishing you in various ways.
• Bounce rate – Refers to the percentage of email addresses in your campaign that didn’t receive your message because the recipient’s mail server returned it. In a different article, we discuss the different types of email bounces, so here, we only remind you that “hard” bounces show that you have invalid emails on your list. If your bounce rate is too high, that might indicate to email providers that you are not collecting your subscribers in the right way, and they might start flagging your domain and content for spam.

Use these metrics to map out what works and what doesn’t. High engagement rates are a sign you’re on the right track, while dips could indicate it’s time to tweak your strategy. On the contrary, you want to keep the unsubscribe, bounce, and reported as spam rates as low as possible. An increase in these metrics should prompt you to reassess your marketing campaigns. 

Your email marketing service might offer analytics tools out of the box, or you can use third-party instruments to measure these metrics. With SiteGround Email Marketing, every email campaign is monitored, and the vital statistics are displayed in a user-friendly and intuitive interface.

10. Send Relevant Content

Relevance is the key to engagement. Your emails should be timely, targeted, and full of value. Personalize your content to resonate with your audience’s needs and interests.

Don’t flood your users with repetitive and irrelevant content just for the sake of sending. Prioritize quality over quantity and make each email campaign meaningful and impactful.

Segment your list to deliver more personalized content. Use data like past purchases, location, or engagement history to tailor your messages. The more relevant your content is, the more likely subscribers are to engage and the less likely they are to report your messages as spam.

11. Bonus Tip: Use Spam Checkers

Before you send out your emails, run them through a spam checker. These tools analyze your emails for common spam triggers and give you a chance to correct any issues before pressing send.

Look for reliable spam-checking tools like Mail Tester and make them a part of your email review process. Incorporate their feedback to reduce the chances of your emails being flagged as spam.

FAQ

Let’s tackle some common questions to help you navigate the world of email deliverability.

Why Are My Emails Going to Junk?

Your legitimate emails could be going to junk for a variety of reasons, including poor sender reputation, low engagement rates, or content that triggers spam filters. To pinpoint the exact reason, you’ll need to analyze your email practices, from the way you collect email addresses to the relevance and frequency of your content.

Take notice of instances when your emails end up in junk and look for patterns. Are there specific types of content that consistently get flagged? Are certain email clients more likely to mark your emails as spam? Use this information to refine your email strategy.

Send Wanted Emails

The golden rule of email marketing is to send emails that your subscribers actually want to receive. This means understanding their preferences, providing value, and respecting their time.

Tune into your subscribers’ wavelength by asking for feedback, conducting surveys, and analyzing engagement data. Adjust your content strategy to align with their interests, and you’ll see better results.

Avoid Email Honeypots

To avoid such spam traps, only collect email addresses directly from your audience through legitimate sign-up forms and never purchase lists. Regularly validate your email addresses to ensure they are legitimate and engaged.

Conclusion

Mastering the art of email deliverability takes time, effort, and a willingness to learn and adapt. By following the tips outlined in this guide, you’ll be well on your way to ensuring your emails reach their intended inboxes. Remember to build a solid foundation with a permission-based email list, authenticate your emails, maintain list hygiene, and always provide value to your subscribers.

As you continue your email marketing journey, keep testing, tweaking, and improving. The landscape of email deliverability is ever-changing, and staying informed is key to success. Implement these preventive measures, monitor your email deliverability consistently, and you’ll find your emails welcomed by both subscribers and their inboxes.