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How to avoid spam filters and reach the inbox

Silvestras
· 19 min read · Email marketing · June 28, 2022

Noticed a sudden drop in open rates? Don’t panic! Your subscribers still love you. They probably just never saw your newsletter in their inboxes. Why?

Plummeting open rates are almost always the result of newsletters accidentally ending up in that nasty place we call the junk folder.

We know your newsletter is not junk. Unfortunately, it can still be flagged and there’s not always an obvious reason why your email didn’t pass the test. But you can be proactive and learn how to avoid spam filters with a few best practices! 


Believe it or not, spam filters are your friend. Unsolicited emails, commonly known as spam, are a huge problem. There are over 200 billion emails sent daily and 59% of those are spam!

An email spam filter is a program that uses an algorithm to determine if an email is spam. Some of these protocols focus on different aspects of the email such as:

Email header

Header filters are used to identify falsified headers, which are firm proof that an email is spam. Spammers don’t want to be tracked, so they include bogus information in the relay chain to prevent recipients from responding or tracking their location.

Content filters

Filters analyze email content looking for words or phrases that may suggest spam. They utilize mathematical algorithms to analyze a message's content and compare it to records of the user's genuine emails and spam messages.

User-defined filters

User-defined spam filters use the feedback of users to build a database that can be used to identify spam newsletters. Every time a new email is reported as spam, its identifiers are recorded in the central database.

Blocklisted addresses

Blocklist email spam filters prohibit emails from senders who have been added to a spammer's list. Because spammers can readily modify their email addresses, blocklist filters are updated regularly.

User permissions

Some recipients set filters that only allow pre-approved senders to contact them. This is to avoid receiving unsolicited spam newsletters. By contacting these email addresses without approval, you can damage your sender reputation and land in spam.

So, how do you prevent emails from going to spam? 


Example of custom domain email sender information

It’s perfectly fine to send emails to your friend or colleague from domains like @gmail.com, @yahoo.com, @hotmail.com, etc. However, when it comes to bulk email delivery, it is not a good idea.

To prevent emails from going to spam, you should always send newsletters from your own domain email that matches your website domain name.

Why? Because MailerLite works closely with email clients, such as Gmail and Yahoo Mail, to whitelist your domain or IP address. If you send bulk emails from other domains, you are running the risk of sending your newsletters straight to the junk pile or landing on a blocklist. Spammers will send phishing emails from domains that aren’t their own. So if email client algorithms can’t determine your identity, they may assume you’re sending spam emails.

You should also avoid making frequent changes to your “From” field names, and don’t use strange names like “8wqq823o@yourdomain.com”. Use clear and reliable names like “newsletter@”, “contact@” or “feedback@”.

The best approach is to personalize your address using a real name, e.g. tom@yourdomain.com. It’s much more engaging than something uninviting like “noreply@yourdomain.com”.

Personalization is important in email marketing, in the guide below we'll explain why.

MailerLite's account settings for email domain authentication

Domain authentication is a method to legitimize your bulk sending domain with our servers so they can send emails on your behalf. You can authenticate your domain by adding new DKIM and SPF records to your DNS panel. This helps email spam filters tolerate your bulk mailing and validates your domain. Domain authentication is a sure-fire way to prove to email accounts that you’re sending legitimate emails.

We wrote a short guide on how to authenticate your email with MailerLite.

Sender reputation is a score given to a sending domain based on the quality of email campaigns, their frequency, size, and subscriber engagement.

To put it simply, your sender reputation is like your Uber rating. If you’re polite and follow all the rules, you get 5 stars. If you’re rude or make a mess, your rating goes down.

3 key events that negatively impact your sender reputation include:

  • Spam complaints: When users report or mark your email as spam

  • Email bounces (hard and soft): When recipients on your email list don’t exist, don’t provide permission to receive emails from your domain, and more

  • Spam traps: Email addresses used for the sole purpose of catching spammers. Any messages sent to these addresses are considered unsolicited

Tip: The best way to maintain a high email sender reputation is to follow the practices outlined in this article.

An IP address is a string of numbers that identifies your computer network’s identity and location. IP reputation is a metric that determines how trustworthy a network is for information and communication.

When using an Email Service Provider (ESP) like MailerLite, users are either using a shared IP, or a dedicated IP. The benefit of using a dedicated IP address is that there’s no user activity (besides your own) that affects the IP reputation.

Dedicated IPs require “warming up” which involves sending a low volume of emails on your dedicated IP and then systematically increasing your email volume over a period of time. If the sending volume decreases below 50,000 emails per week, the IP reputation will begin to suffer.

The benefit of shared IP addresses (using default ESP servers) is that the onus isn’t on you to maintain the heavy sending volume required to keep a good reputation. You can send a single email per month and still maintain a good IP reputation.

When choosing an ESP, it’s important to take into account how they manage and maintain the reputation of their servers. For example, at MailerLite we review all accounts before they’re cleared for sending and continuously monitor activity on our servers to ensure that they’re optimized for deliverability. This is, in part, why we rank first in email deliverability among our competitors.

Tip:  Email tool tester is an excellent resource when choosing an email marketing platform. They periodically test and review the deliverability of a number of ESPs.

Spam filters don’t have the human ability to analyze email copy in context, so they basically flag any email characteristics associated with spam.

How to optimize your email copy to avoid spam filters:

  • Keep it short. In addition to email providers clipping your content, email spam filters also don’t like newsletters that are a mile long. There is not a perfect newsletter length. But if you have more than 200 words or the reader has to work hard to get through it, shorten it

  • Don’t use too many exclamation points!!!!!!!!!!!!!

  • Avoid writing text in red

  • Make sure you are not writing in ALL CAPS. IT FEELS LIKE YOU’RE SCREAMING!

  • Use spellcheck to ensure your email is written correctly

While there are no magic keywords to improve your email deliverability, you can limit the use of risky words to reduce the chance of emails going to spam.

The main thing you want to avoid when writing emails is sounding:

  • Desperate

  • Pushy

  • Outlandish (too-good-to-be-true)

Desperate Pushy Outlandish
Please click here Action required 100% free
Don’t miss this! Act now 0% risk
This is not spam! No catch Win $$
Promise you No strings attached Save big
Please read Can’t live without Cash bonus

When spam filters were first built to detect spam phrases, spammers got around this by creating image-only emails. As a result, if your newsletter template has more images than text it’s more likely to land straight in the spam folder.

Additionally, many email clients don’t display images by default (For example Outlook and Gmail) unless the recipient sets images to display by default, or adds the sender to their address book.

Spam filters can vary from client to client, but to ensure maximum deliverability keep your image-to-text ratio around 70-30 in favor of text.

Every domain you link to in an email has a reputation. If you link to a domain with a bad reputation, it will impact your sender reputation. This is because sender reputation is largely determined by domain reputation. So when you link to dubious external sites, your sender reputation is influenced by association.

To protect your link quality:

  • Link only to legitimate sites with reputable domains

  • Don’t use link shorteners like bit.ly and TinyURL

  • Check your affiliate links to ensure that they’re above board

  • Enable double opt-in on your signup forms—turn bots away at the door by enabling double opt-in on your sign up forms

List of link quality checkers:

The best way to understand your customer’s email experience is by sending yourself the exact same email beforehand. Even if you created your newsletter using a template, it’s always a good idea to send a test email.

Sending yourself test emails allows you to review the campaign’s layout and readability. It also allows you to see if your campaign lands in the promotions folder or spam.

To find out why your email is going to spam instead of inbox, you can use a newsletter checker like Inbox insights from MailerCheck to find out exactly what is increasing your spam score. 

Inbox insights report example from MailerCheck
Image credit: MailerCheck

Instead of manually checking for hundreds of spam words and other factors, Inbox insights does the job for you. Inbox insights provide an inside look into your newsletter metrics before you send it. That way, if needed, you can tweak exactly what needs to be adjusted rather than overhauling your entire email marketing campaign.

Purchased lists are like ticking time bombs. Sooner or later they will destroy your reputation. Filled with non-existing email addresses and spam traps, they quickly inform mailbox providers that you like to break the rules by sending unsolicited emails.

Your messages will end up in junk folders. Even worse, you may be marked as a spammer.

To send an email using MailerLite, the email recipient must be someone who has specifically asked to receive your emails by opting in or signing up in some way. If you are an online business, it can also be someone who has bought a product or service from you in the past 18 months.

When people unsubscribe from your newsletter it's always a little disappointing. However, you must let people unsubscribe by offering a clear unsubscribe link in every newsletter. 

If you don't, you risk the chance that people will mark your email as spam because they don't see any other way to unsubscribe from your emails. So be a good human and make sure the unsubscribe link is part of your newsletter layout. It'll be worth it.

Turn unsubscribes into something positive

Sure you'll end up with one subscriber less on your list, but you can give a positive twist to unsubscribes. When you add a survey to your unsubscribe page, you can collect feedback and take notes on why people are no longer interested in your emails. With each unsubscribe, you now at least get the opportunity to improve your email marketing.

Your email subject line is crucial for your open rate, but it's also an important part of reducing spam marks. People can take a quick look at your subject line and decide to mark it as spam. That's why we advise you to put some thought into your subject line. You can use the tips mentioned earlier (avoid all caps, fishy phrases, and excessive use of exclamation marks) to create a risk-free subject line.

In most cases, you'll be more than fine if your subject line is relevant and written with the reader in mind.

Learn how to write a winning subject line in this guide:

The most effective way to optimize your email deliverability is to keep a healthy email list made up of valid and engaged subscribers.

To maintain a high-quality email list, start by using these 4 strategies:

Regularly clean your list using a mail tester (we love MailerCheck). Doing this will make sure all invalid email addresses, like hard bounces, are filtered out of your list. This is particularly useful for email marketers migrating their address book from another ESP (email service provider) to MailerLite.

Email list report example from MailerCheck
Image credit: MailerCheck

A clean list will avoid spam trap hits and reduce the risk of your sender reputation getting damaged. 

Want to learn more about list hygiene? In our article on how to improve your own email deliverability, we'll explain how you can identify and remove email addresses that aren't doing your subscriber list any good.

The CAN-SPAM Act is a law that sets the rules for commercial email. Besides avoiding hefty fines, complying with the rules laid out in the CAN-SPAM Act greatly can greatly improve your email deliverability.

Some of the main requirements outlined in the CAN-SPAM Act include:

  • Tell email recipients where you’re located - Your message must include your valid physical postal address. This can be your current street address, a post office box, or a private mailbox. You can automatically include your company name and address in your email footer in your account settings

  • Tell recipients how to opt-out - Your message must include a clear and conspicuous explanation of how the recipient can opt-out of getting an email from you in the future. Luckily MailerLite will remind you if you forget to include an unsubscribe link in your newsletter

  • Honor opt-out requests promptly - You must honor a recipient’s opt-out request within 10 business days. Luckily, MailerLite handles this for you by automatically removing subscribers who unsubscribe from your active list. But keep in mind that some subscribers may reply to your newsletter and ask to be removed, you will need to remove these subscribers from your list manually

Whitelisting is when an email recipient adds a sender’s address to a list of approved senders so that emails from that address are never filtered as spam. Instead, when a recipient adds an email address to their whitelist, they are verifying that they trust the sender. This instructs the subscriber’s email client to send messages straight to the inbox.

When you ask subscribers to whitelist you, send them a quick set of instructions to make it super easy.


Remember, you are only as good as your reputation. No matter how honest and good-willed your message is, your subscribers will never see it if you get a bad rep. Follow the simple tips above and you will avoid most email spam filters, stop your emails from going to spam, and keep your sender reputation healthy. 

Editor’s note: This post was originally published in January 2015, but has been revamped and updated for accuracy and comprehensiveness.

Silvestras Armonaitis
Hi, it’s Silvestras, a member of MailerLite’s customer support team. As the first remote employee to join MailerLite in 2014, I was the guinea pig to test if remote work was a good idea. Today, MailerLite is a remote-first company so the experiment was a success! To all the other remote workers who have joined since—you’re welcome.
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