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How to Stop Emails Going to Spam

Inbox placement rate (IPR) denotes emails that reached the recipient’s inbox rather than ending up in their spam or junk folder. Since 2015, the global IPR has grown from 79% to 85%. This means that only one in six commercial emails miss the target. Would you like to achieve this rate or even improve it for your marketing purposes? Below, you’ll find a comprehensive guide on how to stop your emails from going to spam.

My email got trapped in spam – what is wrong with it?

Let’s say your email campaign covered 1K recipients, and only 600 messages reached the target inboxes. The email was the same for all the recipients, but 400 of them filtered into spam by email service providers. So, whose fault was it? Both the sender and the recipient have a part to play here. 

To reach the inbox, any email campaign has to comply with the requirements set by the recipient’s spam filters. These are a set of protocols that decide whether to let in an incoming message or not. So, it is just an obstacle you need to know how to pass through. And if you’re aware of its working principles, you’ll be able to handle it with ease. 

How email filters work

The success of your email campaign is heavily reliant on filter technology. Filters not only block incoming messages but organize them as well. Today, many email service providers break down your messages by social, commercial, newsletters, and other categories. They leverage specific criteria to evaluate an incoming message and place it to the relevant folder. 

Spam filters work in the same way and assign a spam score to the message. If the score meets a certain threshold, the email will be inboxed. Otherwise, you’ll find it in the spam folder. There is a long list of spam criteria, and it gets modified and adapted every day. The filtering practices are usually undisclosed, but we know that they include the following focus areas. 

Types of spam filters

  • Content – check the content of an incoming message for spam trigger words, malicious attachments, refined HTML code, etc.
  • Header – check the header of an incoming message for infectious or falsified information.
  • Blacklist – check whether an incoming message has been sent from a sender not specified in the blacklist.
  • Rule-based or heuristic – check an incoming message according to user-defined criteria. These may include spam triggers for specific senders, words in the subject line, etc.
  • Permission – request approval from the recipient to accept an incoming message.
  • Challenge-response – request approval from the sender to send a message (by entering a password or another method of authorization).

Spam filters can differ by not only the criteria to be assessed but also how they are implemented. Here are the most common options:

  • Gateway – check an incoming message according to the criteria that the filter considers spammy based on the analysis of the incoming email. Usually, a gateway filter is implemented as a physical server to detect phishing, malware, viruses, and spam. Examples: Barracuda, SpamTitan, IronPort.
  • Hosted – check an incoming message after it was approved by the gateway spam filter. Hosted filters, also known as third-party, use content and reputation criteria to assign a spam score to the email. Examples: Cloudmark, Spambrella, MailCleaner. 

What you need to make a spam-proof email

Combating spam looks pretty simple. But each type of email filter comprises many protocols or rules to be followed. For example, header filters are not limited to the information in the headers. They take into account the reputation of a sender’s domain and IP address, check email authentication policy, and so on. Nevertheless, there is no magic in dealing with spam filters, and we’ll teach you how to make your email campaign spam-proof. 

Part 1 – Impeccable sender reputation 

Domain reputation

Email filters will assess the reputation of your domain based on the following metrics:

  • Complaint rate – how many messages of all emails sent from your domain have been reported by recipients as spam (by percentage). This is the most critical value for your domain reputation and deliverability in general. A high complaint rate is a sign that your email marketing is unwanted – it either targets false recipients or delivers poor value. The optimum complaint rate is below 0.1%.
  • Inbox placement rate – how many messages of all emails sent from your domain have been inboxed (by percentage). This metric is more accurate than the delivery rate because it counts only inboxed emails. The optimum IPR is above 80%. 
  • Spam placement rate – how many messages of all emails sent from your domain have been trapped in spam (by percentage). Your goal is to reduce this metric as much as possible. The optimum spam placement rate is below 10%.
  • Hard bounce rate – how many messages of all emails sent from your domain have been sent back due to an invalid or non-existent recipient address (by percentage). This metric is more valuable than a soft bounce rate that counts the rejected emails due to a short term issue (full mailbox, server down). The optimum hard bounce rate is below 2%.

Domain or email authentication

Authentication is another vital element of your domain reputation. It is a must-have thing for any legitimate sender to protect the domain against phishing and spoofing. Email authentication rests on three widely adopted standards:

  • SPF – validates whether an IP address is authorized to send emails from a particular domain
  • DKIM – authentication of emails using keys for signature-verification
  • DMARC – email authentication using SPF and DKIM standards

IP address reputation

Blacklist is a crucial metric for measuring the IP address reputation. You should not be listed in any blacklist from BRBL to Return Path. If for some reason you have been, make sure to launch a blacklist-removal process. The most challenging thing here is to find out the reason.

Apart from that, some email filters consider other metrics like complaints, spam trap hits, rejected messages, and so on. The type of IP address, dedicated or shared, is also important.

  • Dedicated – one sender is responsible for the IP address reputation
  • Shared – multiple senders are responsible for the IP address reputation

Hence, it is advisable to opt for the dedicated option if your email campaign exceeds 500K emails every week. 

A new IP address is like a brand new car –  it needs a break-in period. Email service providers apply restricting measures to new addresses to combat spammers. As a result, if you send a high volume of emails right away, a significant batch may get to the spam folder. Hence, you should load your new IP address step by step. Once you show consistent traffic, your ESP will identify your IP address as legitimate, and the restriction will be off.

Tools to check the sender’s reputation

  • Sender Score by Return Path – a popular tool to assess sender reputation and find out how email service providers view an IP address.
  • IP Reputation Monitor by GlockApps – lets you check whether your IP has been blacklisted or not. Also, you can use the tool to delist your dedicated IP address. 
  • Barracuda Reputation System – a tool to check your IP address and domain based on a real-time database of IP addresses with poor and good reports.
  • Email Reputation by Cisco’s Talos – check your reputation by three score ranking: Good, Neutral, and Poor. Neutral means that messages sent from the domain or IP address may still be filtered or blocked. 

Part 2 – Polished email content

Some time ago, the content was the primary catch of spam email filters. They checked incoming messages for spam trigger keywords, blacklisted links, and other inappropriate elements. Today, the content check is of lower priority than the sender’s reputation, but content filters are still actionable.

Subject line

  • Avoid promotional keywords like buy/sale/discount in subject lines
  • Words typed with all capital letters are bad manners
  • Exclamation points are no-go
  • Focus on what may trigger the recipient’s interest like features or specs of the product/service you promote 
  • Personalized subject lines can boost the open rate by 10% 

Pay particular attention to this element of your email campaign. With a weak subject line, you will still be able to pass spam filters. But a recipient can mark your email as spam which will impair your sender reputation. 

Body text

Recipients tend to distrust in unreadable and grammatically poor text. Besides, content filters may put your email campaign to spam if the number of spelling errors in your body text is high enough. Therefore, make sure to check grammar and proofread your body text. Readability is also crucial for positive recipient engagement, so mind that too. 

If you combine a plain text with an image in your email campaign, keep a balanced content ratio – 60% plain text and 40% image. The thing is that spam filters may catch an email if they cannot scan the text due to large images. 


It is a regular practice for email marketers to send multi-part messages that contain both plain text and HTML. The latter lets you improve the engagement of your emails and make the content eye-catching. And here, you have to be cautious as well. An HTML section that has formatting errors or broken tags is a sure way to the spam box. Always check your HTML content before sending it.


It was already mentioned that an embedded image should not exceed 40% of the total message body. Also, it might be useful to avoid heavy images at all. As an alternative, you can compress the image and link to it on your web server or any credible service. This will decrease the message size and accelerate the processing and loading of the email campaign. 


An attachment is a red flag for email filters. Solid email filters will put a commercial or transactional email with an attachment in spam right away. So, the best you can do is to provide a link to a particular file placed on your website or another credible location. 

Media content

Abuse of media content in your email campaign increases the spamminess of your message. Besides, it reduces the recipient’s engagement. If there are some media your campaign can’t do without, add a link to it. Also, avoid dynamic scripts – spam filters won’t let them in.  

Tools to check email content

In this blog post about email testing tools, you’ll find a comprehensive selection of email content previewers and checkers. Some services like Litmus or Email on Acid are full-fledged email preview tools. HTML Email Check or PutsMail focus on HTML content only. To check your subject line, you can opt for Email Subject Line Grader or Send Check It. Hemingwayapp is a perfect solution to validate your text readability. 

Part 3 – Engaged recipient

If you want high-level deliverability, make sure your recipients are engaged. Intricate email filters do assess engagement, which comprises the following metrics:

  • open rate – how many recipients opened your emails 
  • click rate – how many times a recipient clicked on the link in your email campaign
  • click-through rate – how many recipients clicked on at least one link in your email campaign
  • conversion rate – how many recipients completed the desired conversion goal

It’s most likely that you’re using the same metrics to measure the effectiveness of your email campaign. But before this, you need to be sure that the email will hit the inbox. And here is what you should take care of.

Email formatting

  • An email should open correctly in most clients and devices. Use the preview testing tools to check this.
  • An email should load fast. Avoid large images and dynamic scripts. 
  • Embedding forms are also a red flag for spam filters. It’s better to replace embedded forms with a link or a CTA button.
  • Make sure the message is free of broken links. 
  • Do not abuse colors and fonts. Email filters consider irregular font colors and sizes, as well as invisible text. Even if a message with abused text design passes through spam filters, a recipient is likely to send it to the spam folder manually.

Email branding

  • Use your brand’s name in the “from” header. This reduces the spam complaints rate and increases the open rate. Also, it is a good practice to use a front person as an email campaign sender. In this case, add “from <your brand>” to the header to increase credibility. For example, Patrick Cosworth from Mailtrap.
  • You can brand other elements of your email campaign including subject lines, headers, and even links. This is good for building recognition and sorting the email by folders. 
  • The design and content of your email campaign should be in line with your brand. Also, visual branding is best when it is consistent with the personas you’re aimed at. 


Follow-up is another way to earn the credibility of email service providers. When you follow up with your recipients, you show that you want to engage them. But the balance here is important. Massive email attacks within short periods are suspicious and can lead to the spam folder. Remind about yourself once a week or two (depending on your activity). Also, this contributes to the progress of your domain reputation.  

Do not forget the unsubscribe link

If your email campaign lacks an unsubscribe button/link, that’s also a good way to end up in the spam folder. Email service providers identify bulk emails as spam if no opt-out option is available. This is legal due to the CAN-SPAM (Controlling the Assault of Non-Solicited Pornography And Marketing) Act of 2003. So, if you think that you can improve the unsubscribe rate by omitting this button or link in your transactional emails, you’re making a mistake. 

Test your email with a spam checker before sending

Let’s say you’ve carried out all the steps above and are ready to launch your campaign. Hold on a second, the last step remains. Pick an email spam checker and test your email. You’ve got many options to choose from including Mailtrap, Mail Tester, GlockApps, and so on. For some spam checkers, you need to send your email to a specified address, and then you get a report. You can view your message, learn how to improve it, find out the authentication and blacklist status, and see if any broken links are there. 

Other tools can assess your email without sending it. Just paste all the content of your message including headers and you’ll see what is missing and how likely it is to be trapped by SpamAssassin. Once you’ve managed to reach the highest score, the email campaign can be launched. We hope your IPR won’t fall below 90%. Good luck!

I hope you enjoyed reading our guide on how to prevent your email from getting into a spam folder. This material was initially written by Piotr Malek, Technical Content Writer at Mailtrap Email Delivery Platform. Check the article on the Mailtrap blog.

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