How to Avoid Email Spam Filters - The Ultimate Guide for Marketers

Steven L.
Steven L.
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Email remains one of the most effective marketing tools available for businesses. Startups and multi-million dollar companies utilize email marketing campaigns to reach their target audience and boost sales. So, how is it that if you were to check your junk mail folder, you would find legitimate messages from companies you've signed up for in the past?

The answer lies in email spam filters. They exist to protect users from malicious content and shady marketing practices. Unfortunately, they are an indiscriminate tool that can hurt legitimate marketing campaigns.

We will explain what spam filters are and provide you with actionable tips to help you increase the deliverability of your emails to follow the best practices for successful campaigns.

Table of Contents

What Is an Email Spam Filter?

Often dubbed a "necessary evil" of the internet, a spam filter is a tool to identify unwanted emails and prevent them from reaching a user's inbox. Back in the early days of email, junk mail was one of the biggest problems for users. It included a variety of content – from delightful offers to malicious malware. As such, spam filters were implemented to safeguard against potentially harmful messages.

Today, spam filters are more sophisticated than ever and have become an integral part of modern email platforms. They use various techniques to identify junk mail, including advanced algorithms and machine learning. These filters protect users from malicious content while allowing legitimate messages to pass through.

While the ultimate goal of spam filters remains the same, several different types of filters are in use today.

  • Built-in spam filters: These filters are pre-installed on email providers like Gmail or Outlook. Most of your recipients will likely be using these filters, so it's important to understand how they work and what triggers them.

  • Third-party spam filters: Third-party spam filters are used by many internet service providers (ISPs) and corporate networks to further protect their users from malicious content. These filters usually have stricter standards than built-in filters and can be more difficult to bypass.

  • Desktop spam filters: Users can also choose to install a desktop-based spam filter on their computers. These filters offer the same level of protection as other solutions but require manual installation and regular updates.

Best Practices to Avoid Email Spam Filters

Let's look at what you can do to avoid the email spam filters. We'll split this section into two distinct parts. The first will include all the technicalities that go behind sending emails. The second will focus on the content of your messages itself.

Technical Best Practices

Technical things can be nerve-wracking, especially if you like to avoid them due to a lack of knowledge. The good thing about them, though, is that they often only require a one-time setup and then run in your favor. Others may require a quick look periodically, but that's about it.

To deliver your emails in the best possible way from a technical point of view, the following points are especially important.

Use Double Opt-In

This is one of the most important things to keep in mind. You should only send emails to people who have agreed to receive them. Double opt-in means subscribers verify themselves again via a confirmation email after signing up.

It ensures that only people genuinely interested in hearing from you receive your messages. Not only is this the moral, legal, and professional thing to do, but it reduces the likeliness of your recipients reporting you or unsubscribing right away. Also, you'll avoid the problem of bots gathering in your lists, since they won't confirm your emails. This way you don't waste money on worthless contacts and send emails only to active people, which builds trust with spam filters.

Double Opt-in Email HubSpot

HubSpot's Double Opt-In to Confirm Subscriptions

That said, avoid sending bulk emails to large lists of unknown contacts. Cold emailing seems like a decent way to increase leads and conversions, but it can also quickly raise red flags with spam filters.

Double-Check Common Blacklists

Since there are multiple email providers and services out there, blacklists were created to standardize the process of flagging suspicious senders. Most providers will refer to these blacklists to determine whether to filter out content from particular sources. These blacklists (such as Spamhaus) will show whether your IP address or domain has been flagged as suspicious.

It is relatively easy to check whether or not you are on one of these lists. Simply go to the blacklist's website and enter your IP address or domain name into the search bar. If you have been unjustly flagged, you should contact the listing provider and dispute the listing.


To prevent future blocklisting, many companies ask their subscribers to "whitelist" their email addresses. Their emails will therefore always bypass spam filters and will be delivered straight to the inbox.

Use a Reliable Email Service Provider

It’s essential to use a trusted and reliable email service provider (ESP). This includes anything from email marketing software to SMTP relays. Your software must have its own set of measures in place to provide great deliverability.

In our independent tests, the following three email marketing software providers performed best in terms of email deliverability:

  1. 1

    - Inexpensive tool for newsletters and basic automation

  2. 2

    - Powerful marketing and sales automation suite

  3. 3

    - Best newsletter tool based on Amazon SES

Besides the standard deliverability of providers, the features of providers are also important to get more out of it. Here, ActiveCampaign has a clear edge, since you can use a spam check and even predictive sending on higher plans in addition to domain verification (which all three options allow).

However, since deliverability is not everything, you should use a tool that suits you in terms of price and general features. Check out our comprehensive research on the best email marketing software.

Include an Unsubscribe Button

People have a right to opt out of your email list if they no longer wish to receive communications from you. Including an unsubscribe button in all your messages is essential. Instead of reporting or blocking you, people can simply click the link and be removed from your list. This way, you ensure spam filters do not receive negative signals, and uninterested users are filtered out.

Unsubscribes should be processed immediately. When someone clicks the link, their email address should be taken off your list without any additional steps required.

Monitor Vital Metrics

During and after your campaign has been sent, you should monitor a few metrics to ensure everything is running smoothly. These metrics include the number of emails sent, open rate, click-through rate (CTR), bounce rate, and spam complaints. This data can indicate how well your emails are performing and whether or not any changes need to be made.

It is also important to note the difference between hard and soft bounces. Hard bounces are caused by invalid email addresses and should be removed from your list, as they will only cause more issues in the future. Soft bounces, on the other hand, occur when a message cannot be delivered due to a temporary issue on the recipient's end (such as a full inbox). These can usually be safely re-sent after a few days.


As guidance, Campaign Monitor points out that the bounce rate of a permission-based campaign should typically remain below 2%. Here you can learn more about high bounce rates.

Send Emails to Active Subscribers Only

Are you proud of the sizable email list that you have gathered over time? That's great. However, be wary of sending emails to inactive subscribers. If they haven't opened your emails in the past few months or even years, it is likely that their email addresses are invalid, have been abandoned, receive your messages in their spam or they simply delete all of your emails. Sending messages to these inactive users can send negative signals to spam filters, resulting in high bounce rates, and ultimately get you flagged as a spammer.

It is best to remove inactive subscribers from your list and only send emails to active ones. That's also why you should refrain from buying email lists from third-party sources. These can contain a lot of invalid and even malicious email addresses, which will harm your overall sending reputation.

Your email marketing software can help you automate this process by setting up personalized functions. For example, through marketing automation, you can tag your subscribers in the background according to their activity level and automatically remove them from the list if, for example, they haven't opened your last 6 emails or haven’t been active for a specific time.

Learn how this works with ActiveCampaign:

Use a Proprietary Domain

You might have a personal email that ends like this:,, or another popular domain. When sending out emails for marketing purposes, it is recommended to use a proprietary domain that is associated with your company. For example, if you have a website called "," you should create an email address like [email protected]

A personalized domain can positively affect your emails and make them appear more legitimate. As a bonus, when recipients whitelist your domain, all emails sent from it will be treated as legitimate and won't end up in their spam folder.


Advanced Tip: Create a subdomain like [email protected] from which you send your emails if you are concerned about the reputation of your main domain and want to ensure that your marketing emails have a separate reputation.

Warm Up New IPs

Two types of IPs are usually used in email marketing campaigns – shared and dedicated.

Shared IPs are often the default of any email service that you’re using. It’s cheaper but can be risky as you don't have control over who else is using them and how they are controlled. If someone else sends out spam from the same IP, your emails might also be flagged as suspicious. However, shared IPs have the advantage of being “warmed up”, which means they already have a reputation based on the traffic and behavior of the various users sharing that IP address. This often comes with higher deliverability of emails, smoother traffic flow, and lesser scrutiny from spam filters, as opposed to a “cold” IP, which has no established reputation. Overall, shared IPs are better for better suited for individuals and small to medium-sized businesses.

On the other hand, dedicated IPs are more expensive, but they provide a solution to security issues. The only problem with dedicated IPs is new ones will not have a track record. Much like a lack of credit history can affect your ability to get loans, a lack of track record for an IP address can cause email providers to flag it, especially when sending in bulk.

For new IPs is important to warm them up before sending out large email volumes. Start small and gradually increase the volume of emails sent to build up a good reputation for your IP address so it won't be flagged as suspicious.

As for email marketing software providers, they use shared IPs and therefore have some control over how your reputation is managed. Often you can switch to a dedicated IP for an additional charge, but this is only recommended if you send over 50,000 emails per week. The reason for this is the warm-up process and maintenance paired with the higher costs, which are usually only worth it at higher volumes.

Therefore, we recommend using software that has a high delivery rate to begin with, as they are bound to have a good reputation.


Domain and IP reputation are two different things, which are both important. As with a dedicated IP, you should build up the reputation of your email domain steadily and not send bulk emails right away. For more details about whether a dedicated IP or shared IP is best for you, check this article. And for more tips on warming up a dedicated IP visit this one.

Set Up Authentication Records

Speaking of bulk emails, spam filters will also look for authentication records to filter emails. Authentication records are essentially a way to prove that you are who you say you are, preventing impersonators and fraudsters from sending out malicious emails from your domain.

Setting up SPF, DKIM, and DMARC records can help boost your reputation with mailboxes and ensure that your messages don't get flagged as suspicious or end up in the spam folder.

The two most common types of authentication records used by email marketers are Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). You can set up these records for your emails through most hosting providers' Domain Name Systems (DNS). Domain-based Message Authentication, Reporting, and Conformance (DMARC) is an additional email authentication protocol that builds on SPF and DKIM to further protect your domain from unauthorized use.

Email Authentication Records

All three technologies are used to verify the identify of the sender

Note: The best email marketing tools offer you the possibility to verify and manage your domain easily.

Familiarize Yourself with CAN-SPAM

Established in 2003, the CAN-SPAM Act is a set of laws governing how companies send commercial emails. It's essential to familiarize yourself with these regulations to avoid running afoul of them when sending out marketing campaigns.

The most important points to remember are:

  • Make sure you have an obvious way for people to unsubscribe from your emails.
  • Don't use false or deceptive subject lines.
  • Get permission from customers before sending them any emails.
  • Include a physical address in your emails.

You should also be on the lookout for any new laws that may be enacted in the future. Keeping up with changes to email marketing regulations will help you stay compliant and avoid any legal issues.

Understand Blind Carbon Copies (BCCs)

When sending the same email to multiple recipients, never forget to use blind carbon copies (BCCs). BCCs hide recipients' emails from each other, preventing them from seeing the contact list. Besides respecting people's privacy, this is also important from a spam filtering standpoint as it helps to avoid your emails being flagged as suspicious.

Always use BCC instead of the CC option when sending out mass emails directly through an email client like Gmail or Outlook.

Find the Ideal Frequency for Sending Emails

If you only send one email per year, your subscribers will likely forget who you are and won't open your emails. On the other hand, if you start sending out too many emails out of the blue in a short period of time, you may get flagged as suspicious and end up in the spam folder.

The ideal frequency for email marketing campaigns will depend on your industry and subscribers' engagement. As long as your KPIs (see vital metrics further above) remain reasonable, you can also send daily emails, but if these metrics are suspicious, shift down a gear.

Creating Spam-Proof Content

Most of the technicalities listed above are "set and forget" steps you don't need to consider much after the initial setup. It's a little different with your content because you're not sending the same emails to your contacts.

Here's a checklist of the best practices to avoid spam filters in terms of your content.

Use a Recognizable “From” Name

The first thing you should pay attention to is the "From" field. Upon receiving an email, people will immediately recognize it as a legitimate message if they are familiar with the sender. This is especially crucial when using automated emails such as newsletters and subscription reminders.

Avoid leaving the “From” field empty, or your email address will be visible such as [email protected] or similar variations that make it hard to determine who sent the email. Adding your first and last name, company name, or department + company name can go a long way to ensure people don't think your emails are spam.

Mind the Length of Your Subject Line

When writing subject lines, you want to keep them short and sweet but also informative. A good rule of thumb is to include the email's purpose within 60 characters or less so people can quickly understand the message. Your subject line should inspire curiosity and make people want to open the email.

Avoid Spam Trigger Words & Symbols

There are certain words and combinations with symbols that often appear in spam messages. Spam filters constantly analyze patterns and filter these emails as suspicion increases. This relates to your whole content but in particular to your subject line.

Words like "make money", "free", "exclusive offer", "$$$", and "click here" can get you in the wrong folder when used too often. You can find more examples of spam-triggering words here and here. Watch out for terms that may come across as sketchy, over-promising, and pushy.

This does not mean you can never use these words, symbols, or tonality. But if you use it too often, you can quickly get into trouble, as spam filters will notice a tendency and categorize you as spam over time.

Key Takeaways:

  • Minimize the use of spam-triggering words and phrases
  • Avoid using all-caps (e.g. FREE DOWNLOAD)
  • Don't overuse symbols and punctuations (e.g. $$$, ????, !!!!)
  • Don't use more than 1-2 emojis in your subject line

If you use emojis, make sure they complement words and don't replace them. Some email clients display emojis differently, so test them beforehand.

Limit the Use of Rich Media

Images and GIFs can add a lot of visual appeal to your emails and make them stand out. However, it's important to remember that email clients have limited support for these types of content. Large images take time to load, and if used excessively in long emails, they may be marked as spam.

If you want to display a lot of rich media, such as videos, consider just including a link to an external page where the content can be viewed.

Avoid Sending Attachments

Sending attachments in marketing emails can get you in the spam folder quickly. They are fraudsters' favorite tools when spreading malware and other malicious content.

But it's just a PDF?

Yes, but unfortunately, even PDFs can contain a virus. So try to avoid any kind of attachment. Spam filters are not a fan.

Instead of sending an attachment, use a link that leads to the document where people can view or download the content.

Use Regular Fonts and Colors

Spam filters are cautious of too much styling or unreadable fonts that stand out too much. To play it safe, use a basic web safe font. These are usually pre-installed on most users' devices and can therefore be displayed without problems. The most common web safe fonts are:

  • Arial
  • Helvetica
  • Verdana
  • Georgia
  • Times New Roman

Here you can find more web safe fonts and estimated percentages of compatibility depending on the system. If a font cannot be displayed, your content will be displayed to the user in a different fallback font.

As much as we all want to use the web fonts from our website, chances are slim that every user can see them. Therefore, it is better to choose a web safe font that is closest to the one on your website.

Your text font should also be readable, which means neither too small nor too large. As for colors and formatting, simple is always better. Don't worry, you can still highlight a special offer in red, make important parts bold, or add a list. This is more about moderation. If your whole email is red or consists only of changing styles, it’s not a good sign for spam filters.

Watch Your Spelling and Grammar

This may sound like a joke to you but hear me out. Many spammers are not native English speakers, and their emails often contain numerous grammar mistakes. Alternatively, some of them purposefully use incorrect spelling to avoid being detected. For example, instead of writing "discount," they may write "dis count" to bypass the trigger words filter.

To avoid being lumped together with these bad actors, pay attention to the wording of your emails and double-check them for typos and syntax errors.

Create Clear and Concise Copy

As for the actual content, make it clear and concise. Avoid using too much text and focus on getting to the point quickly. A general rule of thumb is to keep the body of your average email under 200 words.

This certainly doesn't work for every business, especially storytellers, but if you have the option, try to keep it short and rather have your readers click on a link where they can learn more.

Respecting this limit will not only help reduce the chances of your emails being marked as spam but will also make them easier to read and more impactful. Based on 40 million emails, a still-relevant study by Boomerang even found that the best-performing marketing emails have a length of 50-125 words.

Use Legitimate Links

When including links in your emails, confirm they are legitimate and lead to secure websites. Spam filters tend to be suspicious of links leading to unknown or shady websites, so make sure they all pass the credibility test and use HTTPS. Linking to a domain with a bad reputation or many spam reports could negatively impact your email's deliverability.

Make Your Design Mobile-Friendly

Around 60% of global website traffic now comes from mobile devices, and it’s almost the same for emails.

Keep this in mind when designing your campaigns and optimizing your emails for desktop and mobile, as some email clients may decide not to display your content if they cannot render it correctly.

The consequence is logical, if your emails are insufficiently displayed too often, they are more likely to end up in the spam folder. This can happen indirectly due to the suffering KPIs or directly due to more advanced detectors of spam filters.


An email marketing campaign should never be taken lightly. To ensure that your messages reach the intended recipients and are not mistaken for spam, follow the above advice. You'll see a huge improvement in your deliverability and engagement once you learn how to avoid marketing emails going to spam.

AI is on everyone's lips, and you can expect it to be increasingly used for spam filters as well. Therefore, do everything you can from the things we have discussed to avoid attracting negative attention. Ultimately, it will also help you to attract your target audience more effectively.


What is email deliverability?

How can I test my email deliverability?

Are spam and phishing emails the same?

Can I be removed from blacklists?

How can I maintain a good email sender reputation?

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Average tennis player with above-average skills in marketing automation. I’m obsessed with delivering results but also tend to read each marketing email I receive five or more times to analyze it.