Understanding Email Deliverability: How to Avoid Spam Filters When Sending Emails

I don’t know about you, but I love sending greeting cards. I pick out the card, write a personalized note, usually add some money or a gift card, and drop it in the mail for my recipient. 

I would be frustrated if the post office did not deliver the card. But, the USPS has some strict guidelines for sending mail. 

Did I write the correct address? Did I add a stamp? Was my envelope properly sealed? Did I do all the things to make sure that my card got where I intended it to go? 

Email Deliverability is a lot more complicated than sending a greeting card via postal mail, but the premise is the same. If you’ve spent a lot of your time and energy writing the perfect email, it should get to your audience’s inboxes every time. 

And like a lost greeting card, it’s just as frustrating when your email isn’t delivered as planned. In 2024, an average of 16.9% of emails (or 1 in 6!) never make it to their intended recipient. 

Hence today, we’re going to talk about Email Deliverability. We’ll go over what deliverability is, best practices to avoid being marked as spam, and how to maintain your best possible sender reputation over time. 

Why trust me: Working within the email and blog spaces, I’ve learned an incredible amount from experience about what makes great content—and how to stay out of spam.  I took the time to verify everything in this blog was accurate (and learned a WHOLE lot along the way!) 

Key Takeaways 

• Multiple factors can influence your email deliverability, and there is no one-size-fits-all approach to it. 

• Building or repairing your sender reputation can take time. Trust the process.

• Because deliverability can be impacted with each send, you can get the most accurate numbers by looking at your deliverability trends over time. 

• Engagement and authentic content are key factors to stay out of spam filters. 

• Pay attention to your email weight and URLs. Both are reasons that you may end up being marked as spam. 

• SPF, DKIM, and DMARC are important authentication protocols to keep in mind (and required for bulk senders by Google security mandates). 

• Cleaning your email list ensures that your subscribers are engaged and less likely to mark your emails as spam, leading to higher deliverability and better results." 

Understanding Spam Filters and Email Deliverability

Let’s start by first defining what deliverability is, straight from the beehiiv newsletter glossary: 

Sounds pretty straightforward, right? Not so fast. 

Deliverability is actually pretty complicated. The factors contributing to your emails being marked as spam are unique to your individual business and subscriber list. 

Think about the different Internet Service Providers (ISPs) that your subscribers may be using. You send from an Email Service Provider (ESP) that then communicates with an ISP. Each ISP may have a different set of criteria that they are looking at when determining whether your email is legitimate or spam. The ISP uses the reputation of the domains and IP addresses associated with your ESP to then make that determination. 

The factors affecting your ESP reputation could be your emails’ weight or certain common spammy words (more on this later). What may be an issue for your publication’s deliverability on one occasion may not even be the same issue for future sends. 

Further complicating deliverability is that many deliverability issues can’t be solved overnight, or even with your next send. It takes time to build your sender reputation but trust the process. 

If all this sounds scary to you, don’t fret. Building your sender reputation, improving your deliverability, and getting your emails to your subscribers is possible. Even with a deliverability snafu. By focusing on engaged subscribers, using best practices, and utilizing tools like beehiiv’s smart warming to boost the reputation of your domain, you can achieve your deliverability goals.  

Defining Spam Filters and Their Functionality

A spam filter is a program used by an ISP to identify and block malicious content. As an email recipient, spam filters help keep you safe from security threats like phishing emails or malicious, virus-containing links. 

Spam filters work overtime, keeping you and your readers safe from malicious emails. In 2011, Spam emails accounted for 80.26% of all emails sent globally. By 2023, that number had steadily dropped to 45.6%. 

There are likely many contributing factors, such as the increase in regulation, the improvement in spam filter techniques, and the rise of social media. And in 2015, BBC identified part of the reason for the decrease in spam emails as being that spammers simply moved to other platforms.

There are different types of spam filters that your content may get trapped in, and understanding the differences can help you understand how to avoid them all together.    

Content Filters

Content filtering uses filters that look at your content and determine if it is similar to other content that is known to be spam. Content filters examine all components of your email, from the subject lines and body copy to images. 

Content filters are mostly looking for the specific words that you use to evoke emotions like fear or urgency. Ensure that your CTAs are genuine, not manipulative. More on how to avoid spam trigger words later.

Bayesian Filters

A Bayesian filter takes filtering to the next level by using statistical probability determining whether the use of words and phrases in a content piece is likely to be spam. Over time, the filter trains itself to improve by automatically learning and adjusting the probabilities. 

Blacklist Filters

Blacklist Filters look at the known spam blacklists and determine if your domain or IP address has been noted as containing spam. These can be one of the hardest to fix as you need to request to be removed from the blacklist. 

Header Filters

Header Filters look at your metadata to look for inconsistencies. It looks at factors such as your IP address to determine if spam has been sent from that IP address in the past. 

Language Filters

Language filters block emails delivered in a language different from the recipient's preferred language.

The Role of Deliverability in Reaching Inboxes

It may seem obvious, but the better your deliverability, the more likely your email will arrive in your recipient's inbox. 

Setting up Google Postmaster Tools (GPT) is a great way to measure how your newsletter is performing. Google Postmaster Tools measures your sending reputation with insight into deliverability metrics for your Gmail subscribers and offers insight into how your mail may perform with other mailbox providers like Microsoft or Yahoo.

Key Metrics Influencing Deliverability

Here are a few of the metrics to pay attention to to see how your newsletter is performing: 

• Open Rate: The number of readers who opened your email. 

• Bounce Rate: The number of emails that aren’t delivered for any reason. 

• Click-through Rate: The number of readers who clicked a link in your email. 

• Spam Rate: The number of emails that went directly to the spam filter of your intended reader. 

• Soft Bounce: An email returned to the sender, then reattempted later. 

• Hard Bounce: The email has been fully rejected and was not delivered. 

• Spam Complaints: This is the number of reports made against you claiming that your content is spam. 

By themselves, none of these numbers give a clear picture, but together they create a comprehensive view of how your newsletter is doing. 

Common Reasons Why Emails Go to Spam

Most of the time, when an email goes to spam, there is either a technical reason associated with your authentication. One of these common issues that can be easily solved by paying attention and making small changes to your content. 

Remember that while these issues are typically easy to resolve, it may take time for your deliverability to fully recover to its previous level. To accurately gauge your emails' delivery performance, don't focus on individual sends, but rather, consider the overall performance over a longer time frame. 

Spam Trigger Words to Avoid in Emails

As we talked about in the content filter section above, content filters look for certain words or phrases similar to other content known to be spam. This includes words like ‘free,’ as scammers use it to write too-good-to-be-true content. 

The list of words and phrases that could land you in a spam filter may seem daunting with over 200+ keywords to avoid, but it’s best to familiarize yourself with the general categories.. 

To avoid spam filters, concentrate on authentic content rather than ‘advertising’ techniques. Refrain from using words like  ‘Free!’ or ‘Limited Time Offer’ that may create a false sense of urgency. The content that sells your product is genuine and authentic, so use that to your advantage!  

Writing Style Tips to Evade Spam Triggers

When writing to avoid spam triggers, ensure that your content is genuine. Most of the words that can land in spam filters are misleading or suspicious. When you write genuinely engaging content, that eliminates a majority of the words that could land you in a spam filter. 

If you must use words that can land you in a spam filter, make sure that you use them within context, and try to use them as little as possible. 

Keep Email Weight Low

Your email weight determines whether your email will be delivered and whether Gmail or other providers will ‘clip’ the email. If your email is clipped in Gmail, part of your message will be replaced with three dots, which your reader must click to view the entire message.

Doesn’t sound too bad, until you consider that on average, your readers will only spend 9 seconds on your email (Statista, 2022). With Gmail users accounting for just over 30% of email users globally in 2024 (Statista, 2024), that’s a huge segment of your list that may not want to go through the hassle of expanding your email in those critical 9 seconds. 

So what is email weight, and how do you avoid issues? 

Your email weight is made up of two parts, with different target numbers: 

• Weight of the code: This is the file size of the HTML that makes up your email. Each character of HTML is approximately 1-2 bytes. Gmail has a hard requirement of clipping your email at 102 KB maximum for your code weight. It’s a best practice to stay under 100 KB just to be sure – and make sure that you pay attention to this number being KB, not MB. beehiiv will send you a warning if you approach this number, but keeping your email copy short and sweet will help to avoid potential issues. 

• Weight of everything required to load your email: This includes the weight of the code above, plus the weight of everything else in your email, like images, videos, and even things like custom fonts. As a general rule, and to avoid issues with different ISPs, keep your total overall weight 10 MB or under.  

Pay attention to URLs 

URLs can seem harmless, but they often have a higher weight than what you realize. This is most especially true if you’re using a link shortener or branded links. It’s a best practice to keep links to a minimum because they can quickly drive up your code weight, leading to decreased deliverability and email clipping.

URLs can also be an issue when you link to external websites. Verify your links and the links of other sites you link to. Ensure that you’re only sharing links that you can verify are safe, and who are trusted to be stringent in the sites that they link out to. 

Avoid spam filters by only posting links to sites that you trust. Remember, your subscribers trust you, and each link you send them should be scrutinized to make sure that it is safe. Take care to avoid typos and check that all of your links are going to where you intended before hitting ‘send.’ 

How to Craft Emails That Avoid the Spam Folder

Writing emails that avoid the spam filter is really about crafting content that keeps your audience interested in and engaged. When your audience opens your emails and clicks your links, this shows the ISPs you’re emailing that your audience not only consented to your emails but actively wants to continue reading them. 

Personalization Techniques to Bypass Spam Filters

Personalizing your emails is a great way to avoid the spam filter. When your emails are personalized and relevant to the sender, they are way more likely to engage and keep your email out of spam. 

The Art of Preview Text Optimization

An email preview text is a snippet of information that appears next to the subject line of your emails. Mastering your email preview text can give you a significant boost to your audience’s attention. 

Craft your preview text in a way that entices your readers to read your email by giving them a taste of what’s to come – then hook them with your compelling content once your email has been opened. And remember, genuineness is key. 

Crafting Subject Lines That Get Noticed

Your subject line is the first impression that your readers will have of your email, so crafting the perfect subject line is critical to engagement.

In fact, according to research, 64% of people open emails based solely on the subject line (Chadwick Martin Bailey, 2024). This highlights the importance of your subject line for capturing your reader’s interest.

Keep your subject lines short, sweet, and to the point, while also using tools like A/B Testing on beehiiv to find out what your audience responds to (and what they don’t– more on this later). 

Technical Aspects to Improve Email Deliverability

If you have optimized your content but are still having deliverability issues, the source is most likely a technical issue relating to authentication protocols. These protocols are in place so that no one can spoof your domain, i.e. send an email pretending to be you, and help keep you and your readers safe. 

Remember that once you correct your authentication, it can take time for your deliverability to be repaired. Try not to look at your deliverability from send to send, rather look at it as an average over time to get your most accurate measure of how your emails are being delivered. 

Importance of Authentication Protocols

In 2024, authentication protocols are not just suggested for bulk sending– they are a security mandate from Google and Yahoo (domains that are likely to make up a large chunk of your sending list). These authentication protocols really only apply on beehiiv if you are using your own custom domain to send or if you are sending in bulk. That being said, it’s good to familiarize yourself with what’s to come as your publication grows. 

Setting Up and Verifying Email Authentication

The great news is– beehiiv handles setting up two of the authentication protocols, SPF and DKIM, for you. Setting up the third authentication, DMARC requires a bit more action from you. 

Google requires that DMARC for anyone sending bulk email, but it is required, as of 2024, regardless of how many emails you send, that you set up DMARC if you’re using a custom domain on beehiiv.  beehiiv’s guide will walk you through the setup process with easy-to-follow instructions so that you can configure your DMARC authentication as painlessly as possible. 

Understanding SPF, DKIM, and DMARC Differences

SPF, DKIM, and DMARC may seem intimidating, but they are important security mandates that help keep you and your readers safe. At their core, SPF, DKIM, and DMARC prevent someone from pretending to be you (and destroying the sender reputation that you worked so hard to build). Here’s a rundown of the different protocols: 

• SPF (Sender Policy Framework): This determines which IP addresses are allowed to send email from your domain. If an IP address that does not match the list associated with your SPF authentication attempts to send mail, the email will not pass SPF. 

• DKIM (DomainKeys Identified Mail): This adds a digital signature to the emails that you send so that your recipient’s ISP can verify the authenticity of your email. If the email sent does not match the digital signature that is expected, the email will not pass DKIM. 

• DMARC (Domain-based Message Authentication): DMARC looks at SPF and DKIM to determine whether they pass. If one or the other or both fail, your DMARC configuration decides what happens next. DMARC is required by Google and Yahoo as a security mandate. You can choose between three configurations that will determine how your mail gets delivered if it is determined to not have been delivered by you. 

  • Quarantine: Your email will be delivered, but to a quarantine folder. The receiver would need to approve the delivery for it to go to their main inbox. 

  • Rejected: Your email will not be delivered and will result in a delivery error. 

  • None: Only monitoring. There will be no action on your behalf affecting your email’s deliverability. 

This is, of course, a very surface-level overview of the topic. If you have any questions about deliverability for your account, speak to a deliverability specialist or reach out to beehiiv support. 

Monitoring Your Deliverability with Reports

As I mentioned before, when you look at your deliverability, it’s important to look at your deliverability as an average over time instead of send to send. We’ve already covered so many factors that can impact your deliverability. With the complicated factors that can come into play, it’s easy to see how the factors impacting a single send may be different than the factors impacting the next. 

When you look at your numbers as an average, you can see a much better representation of your deliverability as a whole. Also, as I mentioned before as well, building or repairing your sending reputation takes time.

Reducing Spam Complaint Rates Through Engagement

Focusing on engagement is the best way to tell the spam filters that your audience wants to read your emails. Engaged followers will open your emails, click your links, and won’t mark your emails as spam. 

When you have a high-quality list that engages with your content, staying out of a spam filter becomes much easier. Those strong relationships that you build with your audience will build your sender reputation as well as your brand reputation. 

Case Studies: Successful Strategies to Stop Emails Going to Spam

Avoiding getting caught in spam filters is so much easier when you focus on driving engagement, but how else can you improve your deliverability? 

Improving Open Rates to Prevent Spam Labeling

Despite not fully being accurate (some inbox providers, like Apple, don’t return reliable data), open rates remain a great measure of how well your newsletter is doing. If your emails are opened and read by your readers, it tells the spam filters that your readers want to read your emails in particular. 

A/B Testing Subject Lines for Better Engagement

A/B testing is available on beehiiv for all paid plans and allows you to see what is working and what isn’t. When you A/B test, you can see how your audience responds, and which subject line they’re more likely to engage with. 

Maintaining Good List Hygiene for Better Deliverability

While it may sound counterproductive to remove hard-earned subscribers from your list, doing so ensures that you’re only sending to engaged users who want to continue getting your emails. 

When you clean your list of unengaged subscribers, you remove the people who don’t want to get your emails in the first place– and are so much more likely to send your emails to spam. 

Regularly Updating Your Email List for Optimal Performance

Cleaning your list should be a habit that you do regularly. This will help keep you from accidentally having someone on your list who didn’t consent to be there and ensures that your list is curated with engaged followers. 

The Impact of Email List Segmentation on Deliverability

Segmentation is a powerful tool for you to wield to help make a big impact on your deliverability, and beehiiv offers incredibly advanced segmentation tools that you can use to increase your deliverability. 

Using segmentation, you can personalize the emails that you send, making your newsletter more relevant to that segment of your audience. When your email is more personalized and relevant, your audience is more likely to engage, improving your deliverability. 

Another segmentation strategy involves creating a segment of your audience that hasn’t engaged with your emails in a certain period, generally the last 90 days. Send this segment an email asking them if they still wish to be subscribed to your emails. 

If they don’t answer or even open the email, you know that they are uninterested, and are a no-brainer to clean from your list. 

Best Practices for Ensuring Your Emails are Delivered Successfully

Engaging Content: The Key to Avoiding Spam Filters

I know I’ve said it more than a few times throughout this blog, but say it with me again: engagement, engagement, engagement. 

When your content is genuine and engaging, your audience wants to open your emails. They want to click your links. The more engaged your audience is, the more likely you are to have excellent deliverability. 

Incorporating Feedback Loops into Your Email Strategy

Confused about why your emails aren’t being delivered? Find out straight from the source what your audience doesn’t like about your emails. 

A feedback survey is a great opportunity to learn from your audience what their pain points are. Be transparent, and as you fix the issue, communicate. 

Maybe something doesn’t work as the audience suggested it would. Communicate with them that you tried, and it didn’t work for the ‘x,y,z’ reason. This will only help bolster your audience’s trust in you. 

Avoiding Blacklists: Tips and Techniques

The dreaded blacklists are the worst thing that could happen to your deliverability. You can be removed, but how easily that can happen is heavily dependent on which list you were added to and why you were added. 

That being said, there are a few best practices to keep your domain off of a blacklist. 

• Never buy lists. Not only is buying a list illegal, as the recipients never consented to receive email from you, but it’s also going to be filled with low-quality subscribers who aren’t interested in your newsletter. 

• Validate the emails you do have. Make sure, to the best of your ability, that the emails don’t contain typos. Wherever you can, have your audience type their emails, as opposed to you adding them manually. 

• Use Double Opt-in. Enabling double opt-in naturally filters out low-quality leads. The extra step ensures that the only people signing up for your email are people who are engaged with your content. 

beehiiv Makes Deliverability as Easy as It Can Be

It’s not an exaggeration to say that deliverability is extremely complex with so many factors that can influence how your emails get delivered (this writer learned a LOT just by writing this blog), but truth be told, we’ve hardly scratched the surface. 

That being said, the best practices we’ve talked about throughout this blog will help improve your deliverability– and over time, help build your sender reputation. beehiiv makes deliverability as simple as it can be.

Get started with a free trial of beehiiv today and see how easy the deliverability features can be to use.