Priya Nain
Author: Priya Nain  |  

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If your email open rates are low, it is quite likely that your emails are not making it to the subscriber's inbox but are landing in spam. So you are left wondering, “why are my emails going to spam instead of the inbox, even though I am not a spammer?” You don’t ask people for credit card details and certainly don’t sell some snake oil.

But the truth is that the spam filters don’t know your intentions and they rely solely on how you follow the rules of email marketing. If your behavior mimics that of a spammer, you are also tagged as one of them and your emails are sent to the spam folder.

Email gatekeepers keeping spammers away
Email Gatekeepers

Sometimes, you might tweak a few things while fixing your spam problems and that might just worsen the situation. This will happen if you don’t know what to look at while identifying the cause of your emails going to spam.

So in this guide, we will be covering 7 major categories of why your emails might be going to the spam folder.

7 Broad Classes of Reasons Why Emails go to SPAM

  1. Email content is ‘spam-like’
  2. Email design doesn’t follow the protocols
  3. Spam laws are violated
  4. Domain reputation is poor
  5. IP Reputation is bad
  6. Email Authentication is failing
  7. Email engagement is poor

A lot of factors contribute to the above and here, with this guide, we deconstruct each one of them. If your email is landing in SPAM it is highly likely that you are violating more than 1 law across all categories.

Before that, a quick word on how email delivery infrastructure works.

In order to deal with the email SPAM problem, Internet Service Providers (ISPs) and Email Inbox providers (like Gmail, Yahoo Mail, AOL etc.) rely on SPAM filters, Firewalls and Blacklist directories to keep your inbox free of "Unsolicited” SPAM emails.

I would strongly recommend checking out our definitive guide on email deliverability to learn more about how exactly this works.

To get the most out of this guide, please familiarise yourself with these abbreviations:

ESP - Email Service Provider. By ESP I specifically mean email marketing software (like SendX) that helps you send emails at scale.

Inbox Providers - Companies that provide an Inbox for your emails (Gmail, Yahoo Mail. Outlooks, Hotmail, AOL, Apple Mail etc.).

Spam Filters - Decides whether the email should be present in the inbox, promotions tab, spam folder or whether it should be blocked all together.

IP Address - Internet Protocol Address. In this article's context it refers to the unique public address of the server over which your emails go. This is typically maintained by the ESP.

1. Email Content is ‘spam-like’

Keywords in your email body & subject line

Avoid using spam trigger words in your email. These are the words that have been classified as too manipulative, pushy, sleazy or evoking negative emotions.

With sophisticated technologies like AI and Machine Language, email service providers can scan each and every email to determine if it is spam or genuine.

We have collected a list of 504 spam words you should avoid. You can check the list here.

Spelling and Grammar Errors

This is a reason why most scam emails are poorly written - It is not because the scammer has poor English or he is lazy. It is because a poorly written email self selects the most gullible victim.

What would you do if you really get scammed - Report it to the police.

This is a bad outcome for a scammer. They would rather want you to ignore the email Or mark it as SPAM, which is what a poorly worded email does!

Then, it relies on the factor that if you can’t detect their technique of using bad grammar you are probably too gullible or greedy for their offer.

Check out this paper from Microsoft Research that talks in-depth about this topic.

So when you display the same behavior of using poor grammar in your emails, your emails are filtered and sent to the spam folder.

Here are some other factors closely related to the format and readability of your email that are considered while judging whether a mail is spam or not. Avoid all of these:

  • Poorly Written Email Copy
  • Big Fonts and Flashy Color
  • A lot of Exclamations!!!!! and $$$$$$

Links inside the email

If the links inside your emails point to a suspicious domain or a URL which has been flagged as fraudulent then it is very likely your email will land in SPAM.

This can also happen if you are using an email marketing software and the backend they use to rewrite links (to track link clicks) is spammy.

We at SendX have been very careful with this and our tech stack ensures that your links are not looking suspicious. You can try SendX for 14 days for free and check for yourself.

Using URL shortener in email

A lot of Spammers use URL shortening services like to hide their spammy URL(as they all have access to the same domain and appear the same). Never use generic link shorteners in your emails. However, if you do need to use them, we recommend you use one that allows you to brand the links that you shorten, such as Rebrandly URL Shortener for example

2. Email Design Doesn’t Follow the Protocols

Use of Images

Few tips here:

  • Maintain a balance ration or text to image
  • Avoid image only emails
  • Use alt text when embedding images.

Spammers tend to hide all SPAM trigger words in an image and use the email body for neutral words only. Since most SPAM filters do not process the image it gets past them. So, an email with a really skewed ratio of Image/Text can start getting flagged by SPAM filters.

Some users don't allow images in emails to load. The images in your email won’t show to them, making your email look spammy and getting marked as spam. SPAM filters will take this feedback and over a period of time will start considering most of the emails with a similar signature as SPAM.

Example of email with Alt Text

Non-responsive email design

This in itself will not directly cause your emails to land in SPAM.

But, considering that the majority of emails are now opened on a mobile device the likelihood of users marking your email as SPAM will increase if the email does not render properly.

That's why all email templates inside SendX are responsive by default. Not only that, we have created one of the biggest responsive email templates resources on the web (till date). It's available for free.

Example of non-responsive email design

Example of Non-responsive Email Design

Using iframe tag, flash, HTML forms, unsupported HTML tags, CSS attributes, javascript

Email HTML is NOT equal to Web HTML.

There are a lot of obvious HTML tags and CSS attributes that are not supported by major email clients (major culprit being - Microsoft Outlook).

Avoid embedding forms in your email. The submit button of the form will require you to use JavaScript (which is a problem).

Most email clients simply don't support flash content as it is considered unsafe for something as sensitive as email. Email clients block emails containing flash. You can use GIFs as an alternative to make your emails more appealing.

Spam filters and more importantly firewalls always take a "better to be safe than sorry" approach. So, all your well-intentioned emails with any type of script will go straight to the SPAM folder.

Missing key elements

If you miss adding key elements like  :

  • from name
  • subject line
  • email body
  • plain text version in your email

and the email marketing software doesn't have a check or stop you before sending that, then your emails will go into the spam go into the spam folder.

No subject line is used as a marketing tactic to increase opens but it's not worth taking a hit on your IP reputation and deliverability.

3. Spam laws are violated

Missing Unsubscribe link

All marketing emails need to have a clear way for users to opt-out of them. If you are sending emails to the opted-in list(s) ensure every email going to them has a way to opt out of using an unsubscribe link.

Usually unsubscribe links are present in the footer, but you should include it in the header too. It's not mandated by law (considering you have an unsubscribe link in the email footer) but email providers like Gmail consider this an important signal of reputation. This is how an unsubscribe link in the header looks like:

Unsubscribe link in the Email Header

Unsubscribe Link in the Email Header

  • Malformed From Email address

Issues with the HTML

If your email has different versions of HTML and plain text email or broken HTML, then your emails will go into the spam folder.

Broken HTML will appear sloppy and unreadable on almost all email clients. Not only will users mark your email as SPAM, but it will also alert SPAM filters (they will think you could be a lazy spammer using unsophisticated tools).

Example of email with broken HTML

Email with broken HTML

An important note here - I have seen way too often, marketers copy content directly from Microsoft Word, Excel, Powerpoint, etc. These applications add additional unwanted characters to your message source. Always copy your content to a plain text editor that strips off all such characters.

All templates we offer for free and every template inside SendX is tested to ensure that HTML is not broken.

Email size > 100KB

Email Acid team did a test on email size and this is what they had to say:

We created text-only, HTML emails in various sizes, from 15-650KB.

We found that sending a file size between 15KB-100KB is A-OK. These emails successfully passed through all our spam filters with flying colors!

Deliverability issues began to occur once the email file size was over 100KB. Every email from 110KB to 650KB wound up failing multiple spam filters. Interestingly enough, once the email file size was over 100KB, the number of spam filters that failed each email stayed the same. For example, an email that was 110KB got caught in the same 7 spam filters as an email with a file size of 650KB.

Multiple studies point out that there is a correlation between email size and deliverability. We would recommend keeping emails between 15KB-100KB to ensure healthy deliverability.

Unsafe OR binary attachment

This is an obvious one. Scammers who use email spam frequently use this technique to steal your data. You would see a warning in Gmail like this:

Unsafe email warning

Unsafe Email Warning

4. Domain Reputation is Poor

Your domain (which you use to send emails) reputation plays a vital role in your email deliverability. To borrow an analogy from the finance world, it is a lot like a credit score for your email domain. If it is high, you will get good deliverability.

That said, let's deconstruct what are the factors that contribute to it.

Using a free email address as your From Email address

If you are not using an ESP (like SendX) then you will need your own domain to send emails. The reason you can not use a free email address inside a 3rd party system is that they have strict DMARC policies.

If you have your own domain you can set DMARC policies that will tell receiving servers how to handle emails that have failed the DMARC check.

Using a free email address

Inconsistent Email Volume

This again is the typical behavior of a Spammer. Also, can you think of a legitimate business that will suddenly increase their email volume by 100x?

Sudden changes in email volume are always considered suspicious in the email world.

People marking emails as SPAM

This should not come as a surprise. If people mark your emails as SPAM, your domain reputation will get affected.

When your subscribers click on Mark as SPAM,  a SPAM complaint is logged by mailbox providers like Gmail, Yahoo, AOL, Outlook, etc. notifying ESP's about the same.

Since SPAM complaints are an explicit user signal about unsolicited emails (even a 0.5% SPAM rate is considered really high).

SendX automatically removes all email addresses from your list as soon as we detect they have marked your email as SPAM for the first time. This ensures that you do not send any further emails to those users. We do this to protect the domain reputation of legitimate users.

5. IP Reputation is bad

IP is not warmed up properly

IP warm-up is a process to establish a reputation for a new IP. Or an IP that has not been used for some time. This also makes it difficult to send a lot of emails over a new infrastructure. A lot of ESPs do not warm-up their IPs correctly which leads to poor deliverability for their users. If you are facing such issues there is little you can do about it apart from requesting your ESP to move you to a different IP or switch to a new ESP.

IP Server not configured properly

If the backend of the ESP is not configured with proper email header, authentication parameters, and encryption then the emails will get rejected by Email providers (like Gmail, Yahoo Mail, AOL etc.)

Not having TLS Authentication

Email runs over the top of a protocol called SMTP (Simple Mail Transfer Protocol) which is unencrypted by its very nature. TLS or transport level security provides a mechanism to encrypt email messages which prevent the content being read from entities other than the intended recipients.

You can check this using the email headers when you receive them. If your ESP is not using TLS authentication for their IPs, it will affect their reputation.

IP not having Return Path Certificate

Return Path is a company that provides data and insights to help organizations optimize their email marketing. They also provide certificates (to ESPs) that are used as a signal of better authority by major email providers. Check more details.

Not having an inbox for a "from email" OR "reply-to" email address that is used while sending the email over the IP

Now, there could be a scenario when the domain has inbox BUT the "from email" being used while sending the email does not. A common example of this is <no-reply>@ email addresses.

SPAM filters will know this is an invalid email once your receipts try to reply (because the reply emails will bounce).

You will start seeing a hit to your IP reputation if this happens regularly.

6. Email Authentication is Failing

Email authentication is an important topic if you are using a 3rd party ESP (like SendX). If you are using a mailbox provider like - Gmail, Yahoo Mail, AOL, Apple Mail etc then your emails will be authenticated by default (if everything is set up correctly).

Quite simply, email authentication means - that you (owner of the domain) are giving required permissions to a 3rd party ESP, to send emails on your domain's behalf.

In case you are wondering if it is even possible to send emails from a domain without providing permission (from the domain owner), the answer is YES. You would have seen emails having via <some_domain_name> in the email header like the following.

Email authentication via another domain

If not, go check your inbox and you are sure to find several emails like this. This simply means Johnny Appleseed's domain is sending this email over the authentication of domain. To read in-depth about email authentication I would recommend reading the Email Authentication section of our Email Deliverability guide.

Needless to say, this is not the best way to send emails. And SPAM filters look at such an email with suspicion. A lot of spammers also rely on this technique since they are able to leverage the good domain reputation of the ESP.

Always ask for your ESP to provide email authentication. At SendX, we provide email authentication for free in every plan and strongly encourage our users (during on-boarding) to get their domain authenticated with SendX.

Here are common mistakes we see people make (when it comes to email authentication):

Not adding SPF Records

It stands for Sender Policy Framework. It is an email authentication method to detect forged sender addresses in emails. It is a TXT DNS record entry which allows an IP or a set of IPs or email servers to send emails for you. All emails not originating from these servers will be considered as unauthenticated.

Email inbox providers check this to either reject the mail entirely or send them to Spam of the receiver's email ID (so that no one else exploits you as a sender). It is a best practice not to allow more than 10 servers to send emails on your behalf.

To test this, you can open any email that you received and check the headers and/or the original mail. The "mailed by" domain tells you whether or not the SPF is applied properly. It should match the domain of the from email address.

Check Headers and original email

In inbox providers like Google Workspace, there is a simplified description of the header in the original email stating whether the SPF passed.

SPF records Header in Gmail

SPF Records Header in Gmail

You can also look up for your SPF Records here.

Not adding DKIM Records

It is the abbreviation for Domain Keys Identified Mail. It provides a mechanism to verify that the email message has come from the domain it is claiming to and the message hasn't been tampered with along the way.

This is done using a two-way (private key and public key combination) authentication. The public key is usually supplied by the ESPs (again, in the form of a TXT DNS entry which can be queried globally) and the private key is used by themselves to encrypt the entire or a part of the email, which can be decrypted on the receiving end by using the public key.

If the decryption fails, the receiver knows that either the domain hasn't allowed this email to be sent or somebody in between has tampered the email (man-in-the-middle attack).

To check whether your DKIM is valid, you can check the email headers and look for "signed by".

Check email Headers for Signed by

In inbox providers like GSuite, there is a simplified description of the header in the original email stating whether the DKIM passed

DKIM records in email Header

DKIM Records in Email Header

You can also look up for DKIM here.

Not adding (or incorrectly adding) DMARC

DMARC is a declaration from the sending domain that their owner knows about email authentication and receivers should receive fully authenticated emails (including both SPF and DKIM) originating from them.

It also declares what actions should be done to emails not having the proper authentication. They may include: letting them be or not affecting them, sending them to the spam folder or blocking such emails entirely.

When DMARC is added for any domain, it can be configured so that inbox providers like Gmail, Outlook, Yahoo etc., can send regular email reports as to how many emails were encountered with/without proper email authentication and what actions have been taken.

This can be added directly by domain owners following the steps in Although the absence of DMARC doesn't cause emails to land in Spam folders currently, most email inbox providers are fighting towards mandating this since the domain owners are much more in charge and help fight email spamming globally.

DMARC entry can be checked in the original email data and inboxes like Gmail also provide simplified headers for it.

Using via Domain

If ESP doesn't provide you with authentication/whitelisting details(SPF/DKIM), then they are using their own domains to send your emails. These temporary domains are authenticated by the ESPs themselves.

This means that not only would your emails go over their servers, but also, your email deliverability would depend on the reputation of these via domains which might be used for their multiple clients with variable email sending habits. This could impact the deliverability and open rates of your campaigns heavily.

You can check the "mailed by" and "via" domains to validate your settings.

Check Mailed by and Via Domains

Domain Present in Email Blacklists

Domain blacklists are quite simply a directory of domains that have been involved in suspicious behavior.  

A lot of publicly available blacklists (300+) have been created. SPAM filters refer to one or more of these blacklists.

Check if your domain is in any blacklists.

We proactively help our users with getting them delisted from these blacklists. Do reach out to us for more help in this regard.

Domain Age

This one might sound obvious, but in the email world, this is even more important.

It is much easier to spoil your reputation forever when your domain is young.

This is because - buying new domains and sending SPAM over that is a typical signature of an email spammer. So, spam filters are extra cautious about you in your early days.

If you have maintained good email behavior for years it is hard to damage your reputation until something really tragic (like a phishing attack) happens using your domain.

7. Email Engagement is Poor

The list has inactive members

If a majority of your users don't open your email, email providers have a strong reason to believe that the emails from this domain are no longer adding value.

There is no point in sending emails to a user who does not open your email. You are not only wasting your money but also adding to a poor domain reputation. I can't recommend this enough. Whenever we onboard new customers experiencing low opens, we recommend them to prune their email list, and maintain a valid email list at all times. It would be a good idea to do some in-depth cohort analysis to measure user engagement over a specific period.


From a domain reputation standpoint:

50% email opens for 5,000 subscribers (2,500) > 20% email open for 50,000 subscribers (2,500)

Non-opted-in list

Apart from getting a lot of SPAM complaints and email bounce, people won't engage with your email. So avoid buying lists or scraping emails off the internet.

Not having a double opted-in list

What is better than a Single Opt-In(SOI) list? A double opt-in list (DOI). That said, I must point out that there are valid arguments on either side.

My point of view on this is driven by this simple logic - You don't make money from the size of your list (unless you sell email lists, which I sincerely hope is not the case), you make money when people engage with your emails. DOI leads to better engagement and hence better domain reputation.

Email list size is a vanity metric for most businesses.

Be sure about the value you want to deliver with your email marketing and test out both the SOI and DOI for that. Whichever moves the needle, go for it.

Malformed From Email address

Avoid frequent changes to the From email address field and avoid obscure From email fields like, We strongly recommend our users to use trustworthy email addresses like “feedback@”, “newsletter@”, “support@”, "hello@”, <your_name@> etc.

We can't tell for sure if this goes as a direct signal to SPAM filters but we have seen emails with trustworthy addresses getting much better open rates. Also, weird obscure email addresses can make some users mark them as SPAM (affecting your domain and IP reputation).

Non-segmented campaigns

If you cater to users with multiple interests it is best to segment them based on that and so that you only send relevant emails.

Segments are a combination of (and) and (or) conditions on top of your email lists.

Using segments you can hyper-target your audience.

Segmentation to hyper target audience

SendX has a powerful segment creator to help you do just that. We can help you segment users based on 50+ various attributes like - type of page visited, company name, demographic data such as age, gender, DOB, email opens, clicks. Know more about it by getting in touch with us.

Wrap Up

If a portion of your email traffic is landing in SPAM then you are leaving money on the table.

A portion of your prospects and users are not getting important messages from you like: pricing changes, deal emails, new features, and product updates, upgrade opportunities and a host of other things.

Your revenue is leaking because your emails are landing in SPAM.

But, understanding why your emails are landing in SPAM could be really complicated.

With this guide, we have attempted to lay down all that LAWS that govern the SPAM world.

So, that you are no longer part of the collateral damage in a war being waged against email SPAM.

SendX complies with all the above laws.

In case your emails are landing in SPAM and you are struggling to figure it out all by yourself, reach out to us for help.

Don't leave money on the table, fix your revenue leakage now.


1) What exactly is a spam email?

Spam email is any unsolicited email, which is usually sent out in bulk, and which is irrelevant, annoying and sometimes malicious. A few examples are fake lottery win announcements, get rich quick schemes, and fake job schemes.

2) Why do my emails go to spam?

Common reason for emails going to spam are listed as below:

  • Spam trigger keywords in the body
  • Spammy subject lines
  • Absence of unsubscribe link
  • Unsafe attachments
  • Poorly written copy

3) How can I ensure that my emails don’t go to spam?

In order to ensure that your emails don’t go to spam, you need to adhere to certain rules such as the ones listed below:

  • Send only to opted-in subscribers
  • Explicitly ask subscribers to whitelist your email address
  • Comply with anti-spam laws
  • Proofread your emails to avoid spelling & grammar errors
  • Avoid spam-trigger keywords
  • Send them to a cleaned up list
  • Include an unsubscribe link.

There are quite a few more such rules for this. You can find an extensive list on the SendX blog.

4) How can I know if my emails have gone to spam?

There is actually no way to know whether your email landed in a specific contact’s inbox or SPAM folder once it got delivered. It could have been sent to SPAM by the contact’s email service provider, or the recipient could have manually reported as SPAM, etc.

5) What happens to my sender reputation when my emails go to spam?

If your emails are regularly marked as spam by the recipients, your domain reputation will deteriorate. And based on that, email service providers may automatically send your emails directly to spam.

6) What are the common spammer-behaviors that I can avoid?

Common spammer-behaviors that need to be avoided to ensure that emails don’t land into the spam box are: bad spelling and grammar, image-only emails, and spammy subject lines containing words like “free”, “$$$”, “unlimited” etc.