Aastha Shaw / Updated: March 14, 2025

Emails Going To Spam? 14 Common Spam Email Filter Triggers

Are your legitimate emails going to spam? But unsure of what is causing this issue?

If so, you're not alone.

With the increasing number of spam activities and phishing emails sent every day, email spam filters are becoming more stringent in filtering out any suspicious emails to protect readers from unwanted and fraudulent emails.

And if you are not careful enough your legitimate emails can also get marked as spam leading to poor deliverability which is a major concern for all email marketers out there.

Now let’s have a look at what exactly email spam filters do and if you are doing anything to trigger the email spam filters. 🤔

● What are Email Spam Filters and How Do They Work?
● Why Are Your Emails Going To Spam? What Triggers Them?

1. Emails and domains are not properly authenticated
2. Missing sender information
3. Having a bad sender reputation
4. You are blacklisted
5. Working with a bad email list
6. Poor engagement rate
7. Using misleading subject lines (clickbait)
8. Using spam email filter triggering words
9. Suspicious or too many email attachments
10. Not following HTML best practices
11. Using link shorteners or open URLs
12. Getting too many complaints
13. Not having an unsubscribe option
14. Not getting permission to send

● How To Prevent Emails From Going To Spam?

What are Email Spam Filters and How Do They Work?

Email spam filters work to safeguard our inboxes from unwanted and potentially harmful messages. They act as gatekeepers by scrutinizing incoming emails and identifying those that exhibit the hallmarks of spam to keep them away from the user’s inbox.

These filters operate based on a set of specific rules that may vary depending on the particular spam filter or email hosting server being used.

In general, these email spam filters scan for frequently used trigger words and use various algorithms to assess emails before categorizing them into:

Not spam: Emails that look legitimate are allowed to reach the main inbox.
Spam: Unwanted or inappropriate messages are directly moved to a spam folder. In some cases, the filter may even delete the email to save the user’s time.
Quarantined: When the spam filter is unsure about an email, it is placed in a quarantine folder labeled as Potential Spam. You can then mark the email as spam or not spam, and the filter will usually remember this decision for future emails coming from that sender.

The primary goal here is to keep your inbox free from scams, advertisements, and other undesirable content by analyzing the emails and classifying them appropriately.

Why Are Your Emails Going To Spam? What Triggers Them?

Here are some of the most common reasons why your emails might look suspicious and are directed to the spam filter:

1. Emails and domains are not properly authenticated

Email Authentication authorizes the ESPs to send emails on your behalf, so they’ll appear legitimate with your domain name attached even though they were sent by a third party.

If your authentication isn’t set up properly, spammers can use your domain for suspicious activities and even your future legitimate emails can end up going directly to your recipients’ spam boxes. The most important email authentications are:

DKIM: Ensures your emails are not tampered with in transit (before reaching the recipient).
SPF: Verifies the sender’s IP address against a list of approved IPs.
DMARC: Prevents phishing attempts, by telling inbox providers to quarantine or reject emails that aren’t sent from a trusted source.

Hence, failing to do these authentications makes you look like an untrustworthy sender and stops you from reaching your intended recipient’s folder.

2. Missing sender information

Along with technical domain authentication, it is also important to keep your sender information up to date as email clients and spam filters often rely on it to identify and filter potential spam messages.

Without the sender's name and email address, it can be difficult or impossible to determine who sent the email. In some cases, missing sender information can be a sign of fraud email, making it more likely to get flagged as spam.

Hence, you should ensure that the “Form” or “Reply To” email details match with your sender and authentication information. Also, make sure to add a physical address, especially in case of bulk email sending.

Emails going to spam - common email spam filter triggers that can be the reason

3. Having a bad sender reputation

The IP address you use to send emails has a significant impact on whether your emails will end up in the recipient's inbox or spam folder.

Your sending habits create a reputation associated with your IP address over time, which is tracked by your email provider.

If your IP address was previously used for sending spam or you face a lot of complaints, email bounces, and poor email deliverability, you start building a negative sender reputation. After a while, it affects your IP credibility, and your emails will likely end up in the spam folder.

This is also true when using a shared IP address. If any of the associated senders do not follow proper sending practices, the emails sent from that IP address may also get flagged as spam.

4. You are blacklisted

Sometimes when everything seems to be right, it can be an unexpected case of being blacklisted.

If you have landed yourself in an email blacklist, then any of the emails you send are going to land in the spam folder. This will happen till the time you get yourself removed from the email blacklist.

While it can take some time, you can request the removal of your domain from the email blacklist by identifying and fixing the cause of getting blacklisted.

👉 How to get yourself removed from the email blacklist

5. Working with a bad email list

A bad email list is the easiest way to make the spam folder the permanent destination for your emails and even get yourself blocked.

Why, you ask?

When not given proper attention, your email lists turn into a dump of invalid, spammy, outdated, and low-quality data.

And when you attempt to send emails to these email addresses, most of your emails will bounce back, or bring in no engagement. You can even get marked as spam when you send out irrelevant emails to random people.

All of these result in the vicious cycle of high bounce rates, bad sender reputation, and poor email deliverability.

Not cleaning your email lists on time can make it very hard to save yourself from getting marked as spam.

6. Poor engagement rate

Low engagement rates on your sent emails will lead to lower email deliverability. This happens because many webmail providers consider your email open and delete metrics to decide whether your emails are spam or not.

This means focusing on sending out email campaigns tailored for better email engagement is one of the ways to keep yourself off the radar of email spam filters.

So, you must focus on identifying the cause of low engagement (such as poor-quality email lists, targeting the wrong audience, irrelevant messages, and sending out emails at the wrong time) and fixing them.

7. Using misleading subject lines (clickbait)

The subject line and header information should give subscribers a clear idea of who is sending the email and what it contains.

If a subject line aims at hiding the sender’s identity or deliberately leads subscribers to believe that the message is coming from someone other than the actual sender, it’s a strong indicator of a deceptive subject line or clickbait.

As per the CAN-SPAM Act, it is strictly prohibited to mislead someone with deceptive subject lines. And if you are using subject lines that look over salesy or deceptive you are going to land in the spam folder. Some of the most common scenarios where your subject lines look spammy include:

Using all caps in the subject line to create a false sense of urgency
Using too many punctuations
Creating a very long subject line
Adding spammy words like free, cheap, etc
Misleading content like “Thank you for your order”; “ You forgot something in the office”; “Re: from the last conversation”

If you are doing anything similar you are likely to get stuck in the email spam filters. And even if you pass through the filters your readers might mark your emails as spam for being deceptive.

8. Using spam email filter triggering words

It’s not just your email subject lines that can get you in trouble but your entire email copy is analyzed to decide whether it is a spam email.

If your email copy consists of any of the following spam-triggering words or anything similar, your emails are likely to go to the spam folder.

Some common email spam filter trigger words:

Free	Risk-free	Act now
Money	Limited time	Special offer
Act now	Exclusive	Limited Quantity
Lifetime deal	Urgent	100% free
Save	Click here	Risk-free trial
Win	Call now	Satisfaction guaranteed
Guaranteed	Don't miss out	Money-back guarantee
$$$	Not junk	No obligation
Unsecured credit card	Urgent	Click here to unsubscribe
Weight loss	You are a winner	Promise you
Cash bonus	Miracle	Full refund

9. Suspicious or too many email attachments

For the longest time, spammers have used attachments in the form of PDFs, zip files, etc to insert viruses and send them to users. Hence, email spam filters have started to filter out emails with such attachments.

Now even if you wanted to share something useful with your user in the form of an attachment, unfortunately, it might land in the spam filter. If you don’t want to face the scenario it’s best to add images or embed the content you wanted to highlight directly into the email.

10. Not following HTML best practices

Email HTML best practices refer to the guidelines and standards for creating visually appealing and functional emails using HTML coding.

Some of these practices include using semantic HTML elements, keeping the email's layout simple, testing the email across different email clients, and ensuring that the email content is easily readable on all devices.

Now, why not following these practices can make you look suspicious?

Improper HTML, formatting, etc exhibit the signs of spammers as they don’t have the resources or time to write code and test it thoroughly. So if you look at spam emails they mostly have sloppy HTML and poor formatting with weird content.

If your legitimate emails are not following the HTML practices and looking like the above example, then the chances of these emails going to spam are high.

11. Using link shorteners or open URLs

Spammers are the ones of love free link shorteners to hide suspicious links and mislead users into clicking on them. So if you are using link shorteners in your emails, especially the free ones with random text, then they are likely to land in the spam folder.

Using open links is another common practice observed in spam emails. If you are using too many open links, instead of hyperlinking them to meaningful texts, then even legitimate emails are likely to get marked as spam.

12. Getting too many complaints

When a recipient marks an email as spam, it is the most straightforward way for the ESPs and spam filters to judge that the emails coming from that sender are spam. Any future emails you send to that address will also be directly moved to the spam folder.

If many recipients mark you as spam leading to a high complaint rate, the emails you send out to other recipients also are likely to go into your spam folder impacting your overall deliverability.

13. Not having an unsubscribe option

If your readers find your emails irrelevant to them, or do not wish to keep hearing from you for some reason, then you need to provide them with an easy option to unsubscribe.

Not providing an unsubscribing option will only leave them with the option to mark you as spam, which is going to impact your email deliverability and is definitely worse than losing a subscriber.

Moreover, providing a clear unsubscribe option is mandatory as per the CAN-SPAM Act, and not doing so can get you into more trouble.

14. Not getting permission to send

In many countries, it is against the law to send out emails without the recipient’s permission. So, if you have sent out emails or automated campaigns without obtaining permission first you will be marked as spam by the email spam filters or by the recipients themselves.

You can send out cold emails though, but to avoid landing in the spam folder, your emails should be personalized and should provide a clear option to unsubscribe.

How To Prevent Emails From Going To Spam?

Now that we know what might trigger email spam filters to direct you to the spam filter, Let’s have a look at how you can avoid it, and make your way to the main inbox. Here’s a quick checklist on how you can prevent emails from going to spam:

Verify all the emails before adding them to your email list. This will help you filter out invalid, spammy, disposable, catch-all, and all bad types of email addresses that can affect email deliverability.
Ensure all the authentications are done properly and you have all the right sender’s information in place to build credibility.
Clean your email lists regularly to get rid of accounts that are outdated, inactive, or not engaging with you for a long time. Also, make sure you are removing the emails that mark you as spam or unsubscribe.
Create personalized and meaningful emails to resonate better with recipients to boost your engagement rate and keep away from spam.
Follow all the CAN-SPAM guidelines to make sure your emails are not going against any laws.
Avoid trigger words as much as possible. Ensure your content is honest and useful to naturally avoid spam filters and look trustworthy to your recipients.
Make sure your emails are well-formatted, contain no junk attachments or bad links, and are optimized for all email clients and platforms.

By following these simple steps, you will be able to keep away from spam folders and enhance email inbox placement.

Most importantly make sure you have a high-quality and clean email list if you want to avoid bounces, boost deliverability, and get maximum returns on your email campaigns.

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