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18 reasons why your email goes to spam (+how to avoid it)

Reading Time: 10 minutes

Most marketers believe that emails get sent to spam for reasons beyond their control, but this isn’t true. 

Spam filters can be triggered by reasons both controllable and uncontrollable. These reasons include low recipient engagement, sender reputation, content-related issues, technical considerations, and miscellaneous factors. 

In this article, we’ll take a look at what spam filters are and how you can avoid them, the top reasons why your emails get sent to spam, and tips on how to prevent your emails from going to spam. 

Let’s dive in! 

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What are spam filters and why we should avoid them

Email service providers use spam filters to sort through emails and automatically identify potential spam. Their primary objective is to ensure that recipients don’t get targeted by fraudulent or malicious emails, but a lot of regular, well-meaning emails often get sent to the spam folder because they don’t follow proper email protocol. 

Spam filters work by analyzing every email’s content, images, sender information, and email infrastructure to identify any potential threats. If these triggers are activated, your emails get sent to the spam folder and your domain reputation takes a direct hit.

Why are my emails going to spam?

As already mentioned, there are multiple reasons that emails can get sent to spam, so let’s take a closer look at those reasons:

Low recipient engagement

Low recipient engagement

1. Low open rates or high email deletions without reading
If your emails consistently record low performance metrics such as open rates, or if a lot of readers delete your emails without reading them, spam filters will get triggered.

To tackle this, ensure that you’re only sending emails to relevant customers. You should also write catchy subject lines to compel your readers to open your emails.

You also need to be mindful of the frequency of your emails and the content you’ve sent in the past. If customers start associating your brand with irrelevant emails that are sent too often, they’re more likely to send them to the trash folder and hurt your engagement rates.

2. Marking emails as spam or deleting them after reading
If recipients read your emails and then mark them as spam or delete them, spam filters could be triggered.

Again, you need to ensure that your emails deliver enough value to your customers, and that they look forward to receiving and reading them. 

If you send out a weekly blast with discounts on your products, ensure that you perform audience segmentation and recommend discounted products that are relevant to each customer segment, instead of sending out generic recommendations to everyone.

3. Having inactive or dormant subscribers
Another reason for low recipient engagement could be that you have too many inactive or dormant subscribers in your audience. This can happen when you don’t sort or clean your email list regularly, or if you target users who don’t want to interact with your brand.

Although a large list can feel good, it does more harm than good to keep inactive or dormant members.

Sender reputation

sender reputation

4. Email authentication
Brands need to ensure that emails are properly authenticated via mechanisms like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), or DMARC (Domain-based Messaging Authentication, Reporting, and Conformance), otherwise emails sent out from that domain address may end up in the spam folder.

If your emails aren’t authenticated, they are also susceptible to hacking and phishing attempts. This automatically hampers your domain reputation and deliverability. 

If you’re using Omnisend, here’s how you can quickly ensure that your emails are authenticated with all the right protocols.

5. Bad sending IP reputation
If you send emails from a domain or IP address that has a history of spamming users, your chances of landing in the spam folder shoot up significantly.

If this happens often, your ESP will flag your domain or IP address as untrustworthy, and all emails sent out from those points will automatically land up in spam. They won’t even reach the inbox on their way!

As a practice, you should remove any subscribers who have marked your emails as spam, immediately after they do so.

6. Low sender scores or high spam complaint rates
If too many subscribers mark your emails as spam, your ESP assigns a high spam complaint rate to your brand or domain. High spam complaint rate is the second most common reason for emails to not land in the inbox.

One of the reasons this could happen is because the recipient doesn’t remember subscribing to you. To help prevent this, make sure that your company’s branding is both consistent and visible across all your communications.

If it’s been a while since you’ve emailed your users, start with a small reminder of your relationship, and use language and design that they’ll recognize.

Email content-related issues

Email content-related issues

7. Spam filter trigers.
Email service providers have identified certain words as indicative of spam—these can be words with malicious or fraudulent intent, or click-bait words. Emails containing such words, or too many hyperlinks or images, get marked as potential spam. These include words like “free,” “buy now,” “limited time offer,” or an excessive use of exclamation marks.

But these words are vital for ecommerce emails—they are actionable and create scarcity. Check your inbox, there are plenty of emails with these words. So why didn’t they trigger the spam filter, and how did they get into your inbox?

We don’t think that spammy words alone can harm your email deliverability. But they can compound a problem if you’re showing other spam signals—which is why you need to take a holistic approach.

8. Misleading subject line
Spam filters can get triggered when the subject line is misleading or doesn’t match with the content of the email.

Remember, all your emails convey a story. Each aspect of the email must add up to the story you’re trying to tell your customers, and this starts with the subject line. You need to state your intentions or objective clearly in the subject line so that readers don’t find a disconnect when they read the email.

9. Unclear unsubscribe link
Your unsubscribe button needs to be clear and easy to access.

Underhanded tactics such as nearly invisible fonts, long unsubscribe forms, and empty space before the unsubscribe link will only backfire. Readers shouldn’t experience any problems when attempting to unsubscribe.

You should also include your business address clearly. If you’re apprehensive about including your personal address in every email, you can always get a PO box and list that instead.

Spam regulations have become stricter for physical addresses and unsubscribe buttons, so omitting either of them will almost certainly hurt your delivery rate.

10. Image-to-text ratio
Image-to-text ratio tells you how much of your email should be filled with images, and how much should be filled with text.

In general, image-to-text ratio is more of a B2B sales email issue, and has become irrelevant for promotional emails because email providers have started caching images and displaying them by default. But still, as best practices, we recommend a standard 40:60 ratio visuals to text.

11. Too many URLs in the content
Using too many URLs in the content might signal to your ESP that you’re sending out irrelevant emails with a commercial objective in mind, which might not be beneficial to users.

When this happens, spam filters get triggered automatically and your email reputation drops. So remember to check that you’ve only included limited, relevant hyperlinks (or URLs) in your emails, and that the anchor text or CTA for each URL is descriptive of what customers can expect when they click through.

Technical considerations

Technical considerations why emails go to spam

12. Blacklisted IP addresses or poor sending reputations
Sometimes, your email can tick all the right boxes in terms of the content and sender reputation, but certain technical considerations might activate spam triggers. This could happen if you’re sending emails from an IP address that is on a blacklist or has a poor sending reputation.

Checking your IP’s status to see if it’s blacklisted is surprisingly easy. MX Toolbox and similar services can check your IP against some of the most popular blacklists. While no search engine can cover every possible blacklist, this is a great place to start if you’re still not sure what’s responsible for your low deliverability.

Most reputable email marketing services have safeguards in place to avoid this problem, but there’s always a chance that your platform has been flagged by spam filters.

13. Attachments and large file sizes
To safeguard users from spammers and hackers, ESPs automatically mark any emails with too many attachments or large file sizes as spam.

So if you’re sending an email to a large user base, remember to only attach files that are necessary, and keep your file sizes as small as possible.

14. Incorrect or missing email headers
The email preheader is one of the most important yet overlooked aspects of a good email campaign. Also called the preview text or the email header, preheaders appear next to the email subject line and give customers more context on the contents of the email.

email preheader examples

Email preheaders provide valuable real estate to help your brands tease an incentive, incorporate a CTA, summarize email content, or build curiosity or FOMO.

If you don’t add a preheader, your ESP will do it for you—by including the first few characters of your email content. This might not be relevant for readers, so your chances of landing in spam automatically go up. 

At the same time, just like subject lines, if your preheaders are misleading or incorrect, your subscribers can get annoyed and mark your emails as spam.

Miscellaneous factors

Miscellaneous factors why emails go to spam

15. Overly frequent campaigns
Another reason emails go to spam is sending too many campaigns within a short period of time.

There isn’t a standard benchmark that can be applied to every email sent, and brands need to be closely attuned to their subscriber base to figure out the ideal frequency for their audience.  

16. Inconsistent sending patterns
If a brand is typically sending to 10,000 subscribers and suddenly starts sending to 200,000, this spike will trigger spam folders (because email clients consider spikes as unexpected behavior and spam attack).

Brands need to work on sender reputation warming before sending out emails to a large user base. This involves starting out with a small user base and gradually increasing the number of subscribers.

17. Poorly maintained email lists
Your email lists need to be maintained and cleaned regularly. If you don’t do so, you end up sending emails to audiences who don’t want to receive your emails, and they’re likely to ignore you and they might even mark your emails as spam or delete them.

scheme showing sunsetting frequency example

18. Anti-spam law and regulations compliance
Another aspect brands often overlook is regulatory anti-spam laws, such as the CAN-SPAM Act or the GDPR (General Data Protection Regulation). Under the CAN-SPAM act, misleading subscribers with your domain and sender name is illegal. So, too, is failing email authentication processes due to phishing and spoofing. 

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How to prevent email from going to spam

Now that you know some of the reasons why emails go to spam, you can start adjusting your own practices to maximize deliverability and make sure any message will actually make it to the inbox. This section will cover some of the best places to start if you’re looking for ways to stop emails from going to spam.

1. Give subscribers what they want

Sending too much, too little, and too generic content are three of the top factors leading to unsubscribes and poor deliverability. Unfortunately, every subscriber has their unique preferences, so improving deliverability isn’t as simple as finding the ‘right’ frequency.

Instead, you should consider giving readers more control over their own subscriptions. You can implement this by adding some options to your signup form, allowing your new subscribers to choose the products they are most interested in.

Segmenting your customers and sending the most relevant content to different segments also helps minimize the number of emails going to spam.

2. Implement the sender’s warm-up process

This practice is most needed when you’re switching your email service provider. Every time you switch ESP, it makes an impact on your sender reputation score so you need to warm up your new domain to reduce the risk of being marked as spam.

Here’s how it improves your sender reputation when compared to sending emails to all your subscribers without a warm-up:

graphs showing the impact of sender's warm-up process

Want to learn more about how to maintain your smooth transition to better email deliverability?
👉 Read our in-depth guide on how to avoid spam filters
👉 Read our list of 11 best email deliverability tools

3. Make sure your email is wanted

This means that the subscriber explicitly agreed to receive your promotional messages via email. That’s why lists must be opt-in and GDPR-compliant.

The best way to achieve this is to mention consent in your signup form:

example of opt-in GDPR-compliant signup form

4. Gradually increase sending volume

If you have a large list, starting your email marketing by sending a campaign to all of them at once is a bad idea.

Here’s an example of a gradual warm-up process:

graph showing gradual increase of recipients with a 300K list

5. Keep your contact list clean

If someone hasn’t clicked on your emails in the last 12 months, that subscriber should be treated as inactive and unsubscribed from your email marketing.

Leaving inactive people on your email list increases your chances of being sent to the spam folder, because it reduces your overall engagement rate. You should also gather good-quality subscribers with signup forms instead of buying ready-made lists. 

💡Pro tip:

When you migrate from one ESP to another, at first migrate your best contacts who are actively engaging with your emails and start sending only to them. That way, you’ll gradually transfer your good reputation from one email service provider to another. After a while, you can migrate the rest of your contact list.

Once again, migrate gradually. Start with a small list, then grow the number of email recipients.

Want to keep your contact list clean the easy way? Omnisend offers a quick and simple email list cleaning service. 

Here’s an example:

Omnisend contact list cleaning example


While there are a lot of reasons why emails get sent to spam, they’re often avoidable and easily manageable. Brands need to invest in qualifying every email marketer to be spam-aware and to deploy preventative strategies that don’t trigger spam filters.

To avoid the spam folder, brands need to ask for email consent in an ethical and clear manner. This should be followed up by relevant, spaced out communication that gives customers what they want, while being mindful of the email frequency and content. 

If you’re switching to a new provider or approaching a new audience, remember to practice domain and IP warming. 

You should give your subscribers an easy, clear-cut way to unsubscribe. Not doing so can cause customers to lose trust in you and report your brand’s email as spam, and this directly impacts your sender reputation.

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Richard White
Article by
Richard White

Richard is a Content Marketing Manager at Omnisend. An avid writer, he's said to have been born holding a pencil. Fascinated by all things handmade, if he's not reading or writing he can often be found practicing leathercraft.

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