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One of the worst things that can happen to you as an email marketer is being labeled a spammer.

Not only does it suck, it can have real consequences for your business. You might get blacklisted and lose out on revenue.

While there are certain things that are out of your control — like what algorithms email services use to check what’s spam, there are plenty of things you can do to make sure you’re getting in people’s inboxes.

In this article, we tell you why your email campaigns are going into the spam folder and what you can do to prevent that from happening..

Why Your Emails Get Marked as Spam

Email services all have different algorithms to try and stop spam, but at their core, they all work the same way. They check certain aspects of your email and give it a spam score. If that score reaches a certain threshold, your email is going to the black hole that is the spam box.

Free email services like Gmail and Hotmail have more sophisticated spam filters. They’re so big and have access to so much data that they can use machine learning to figure out what is spam and what isn’t. And while the exact algorithms are not known ( for good reason) in general, spam filters check the following things:

The source of the email

The first aspect spam filters look at is where the email is coming from. The address that the email is being sent from can be a big indication of whether or not something is legit.

If a company uses a no-reply or an admin email to send marketing messages, spam filters are going to think something is fishy.

The sender’s reputation

Just like the source of the email campaign can be a clue whether or not something is spam, the reputation of the sender can be a red flag as well.

If a lot of bad marketing campaigns are coming from the same IP address, filters are going to flag that IP address and anyone sending from it is going straight to spam.

Luckily, most email service providers (ESPs) work hard to keep their reputation intact. They make sure that emails being sent through their service meet minimum standards.

So if you send low-quality emails repeatedly, your ESP can simply block you from sending out any more emails.

Email content

The next thing spam filters look at is the content of the email. When your email is filled with hype, salesy language, and hyperboles, the filter is going to assume it’s spam.

Friends don’t send each other invitations for multi-level marketing schemes or promise to make you a millionaire overnight.

This can be the trickiest aspect of avoiding spam filters. Sometimes it’s easy to figure out what not to say, but when you have to send a sales or promotional email, it can be hard to know if you crossed the line or not.


When you send an email to a friend, most of the time you’re just sending text or an attachment here and there to one or several people — something spam filters are totally okay with. If you’re sending a marketing campaign, though, often times you’re sending emails that contain plenty of HTML, images, and CSS to a much bigger list.

That in and of itself isn’t bad, but to a spam filter those pieces of code can be an indicator that something is up. Spammers and phishing attacks use code to conceal what they’re doing. So if a spam filter notices an email has a lot of HTML and CSS in it, it’s going to look a little closer and see if the code is clean or not.

Clean code means the HTML is very structured and can be easily interpreted by your email client. Bad code, on the other hand, tries to deceive the reader. Here are some examples of bad code:

  • iFrames (made for web, not email HTML)
  • Bad HTML tags
  • Incorrectly nested HTML tags
  • Characters that are not standard ASCII characters.
  • Unclear URLS (using a URL shortener to hide the original link)
  • Text that has the same color as the background (can be used to hide the fine print)

If you’re using the templates your ESP provides, most of these things are taken care of.

However, you still want to make sure that the contents of your email are easily readable and can’t be mistaken for bad code.

Subscriber engagement

If no one is interacting with your email campaigns (that is, not opening or clicking), email service providers are going to assume recipients don’t want your emails.

If your email marketing service monitors engagement, they may suspend or block your sending in order to protect their sending reputation.

In short, spam filters trigger when your email shows signs of being low-quality. Let’s look at some ways you can avoid getting caught in the spam box.


How to Make Sure Your Emails Don’t Get Marked as Spam

Now that we’ve taken a look at some of the things spam filters look at to determine what is spam or not, let’s look at ways you can avoid them.

Avoid Trigger Words

Certain words are red flags for spam filters. People don’t send their friends emails to “buy Viagra” or put lots of dollar signs in the subject line.

If your email service sees these trigger words, it increases your spam score and you’re more likely to end up in the spam section of your subscriber’s inbox.

The full list of spam words would be too long to include in this post, but here’s a small selection of words that’ll increase your risk of landing in the spam folder.


  • As seen on
  • Buy now

Personal finance:

  • Lowest insurance rates
  • Your income
  • Get paid


  • 50% off
  • Join millions
  • #1

Build Your Own Email List

Building an email list of engaged subscribers and customers can be a very hard thing to do. For some, it’s too hard and they resort to buying a list.

While buying a list might have worked in the ‘70s and ‘80s with direct marketing, online is a different story.

A bought email list rarely gives you a good open rate. Keep in mind that multiple people may have bought the same list and spammed users to death.

The graphs above show the relationship between different metrics and how “public” the list is. As you can see, open and click through rates quickly plummet when lists are getting passed around. ESPs and internet service providers can see this as a sign you’re a spammer and they may take corrective action or blacklist your domain.

If you don’t know how to build a list of people who want to buy from you, here are a couple of resources to get you started:

Use Double Opt-in

Building a list of highly engaged individuals is hard enough, but when you use double opt-in it can be even harder.

Sometimes people don’t confirm that they want your emails. Maybe they don’t know what it’s for or they don’t trust it. You might lose out on subscribers doing this.

On the flip side, using double opt-in can increase the quality of your list dramatically. By having to confirm their email, you filter out all the people who entered a fake email to get your freebie, or people who made a typo. It also gives you the reassurance that people actually want your emails.

If double opt in just isn’t your cup of tea, make sure you have a recaptcha tool on your sign up form. This is the safest way to allow legitimate single opt ins that don’t expose a form to the risk of getting spammed by bots. This is when a program runs to just add fake emails to a list repeatedly. Sounds ridiculous, we know — some people just don’t have anything better to do with their time.


Use a Clear “From” Address

According to convince and convert, 43% of email recipients click the spam button based on the “from” name or email address. That’s nearly half your list! So an easy way to come across as genuine is to use an actual email address. And better to use your own domain than a freemail service like Gmail, AOL, or Yahoo. A freemail email can also be a red flag.

If you’re sending from a no-reply email or it has a bunch of numbers and weird characters in it, spam filters are going to think you’re not a real person.

Test Your Emails First

A simple way to see if you’re going to end up in your customer’s spam box is to send a quick test email to yourself. If you’re sending an email with a good balance of text and images that contains valuable content and a non-spammy subject line, your chances are slim that you’ll end up in the spam box.

Use a Reputable ESP

A good email service provider will have solutions for most of the problems listed in this article. They work hard to protect their own reputation and will hold their customers to a certain standard.

Write Good Emails

The single most important thing to worry about is to write good emails. They should be relevant to your customer’s interests and provide them with quality, valuable content. If your emails are worth checking out, you’ll have no trouble reaching your audience.

Clean Your List Regularly

Email lists decay after a period of time. Users lose interest, change email addresses, sometimes they don’t know how to unsubscribe and mark your emails as spam to get rid of them.

Whatever the reason, you don’t want these people on your list. Not only do they cost you money, they can also have a negative impact on your sending quality. Open rates go down, emails start bouncing, and your email list just seems less responsive.

To fix this, clean out all the email addresses that are not reacting in any way with your email for a longer period of time. If they haven’t opened an email in 6 months, chances are pretty high they’re not interested anymore (Robly has an extremely nifty tool that makes this as easy as possible).

You can always send an email first that says you don’t want to bother them any longer and that you’ll unsubscribe them unless they click a link.

If they click, you know they’re engaged. If they don’t, you can safely unsubscribe them

Provide a Clear Unsubscribe Link

This should be common sense by now, but every now and then you get an email where the unsubscribe link leads to a page that doesn’t exist or that doesn’t work properly. This is not only a shitty thing to do, it’s also illegal.

People who want to unsubscribe aren’t going to buy from you anyway, so just let them go. If you’re using an email service provider, this should be taken care of for you. If it’s not, run.

Make Sure Subscribers Remember You

As more businesses discover the value of email marketing, it’s becoming harder to stand out in inboxes. People get dozens of messages each day from different companies.

If they don’t recognize your name they are more likely to hit that spam button.

The best way to prevent this is to email subscribers as soon as they sign up (with a clear From name, of course), followed by content on a regular basis.

Here’s an example:

If you consistently send relevant content, subscribers will remember your name and are more likely to open your emails.

Ask Subscribers to Whitelist You

If you ask your subscribers to add you to their address book, your emails have a higher chance of getting to them.

The tricky part is asking the right way. If you just ask them by sending a random email, it’s not going to work. The best way to ask is immediately after they’ve signed up. On the Thank You/Subscription Confirmation page, show them how to add someone to the address book.

The added benefit is that for Gmail users, you’ll land in their priority inbox, not the promotions tab.


Writing good emails is hard enough as it is. Don’t let all your work go to waste by sending emails that go straight to the spam folder. We all receive plenty of spam, so a good rule of thumb is to look at all of those spammy emails and don’t do what they do!

Follow the tips in this post, and you’ll be well on your way to sending emails that have great deliverability.

Robin Geuens is a freelance content marketer who helps SaaS businesses write content that gets more traffic, subscribers, and leads. You can find him at

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