Spam Filters: What They Are and How to Pass Them

Spam Filters

Table of Contents

If you are doing email marketing, we are sure you are always struggling to pass spam filters and reach the inbox. Don’t worry, we know that feelings.

Everyday, worldwide companies and brands, adjust their campaign to reach the inbox of their users. In fact, according to ReturnPath, 21% of emails sent with permission still end up in the spam folder. 

In this article we will see what spam is, how spam filters work and how you can pass them.


What is spam?

First things first, let’s understand what is spam.

Spam is unsolicited and unwanted email sent to a list of contact. They are emails that addressees never ask for, or they can also be email with dangerous content (e.g. malware and phishing). 

There are severe laws against Spam. They change according to every country and you should be aware of them all. This is particularly important when it comes to an international business. 

Some of them are the: CAN-SPAM Act and the Canada’s Anti-Spam Legislation (CASL). If you work in the European Union, you can find here all the Anti-Spam Laws you should know


What are spam filters and how do they work?

Spam filters are, as the word says, filters that allow users to receive in their inbox only safe emails. They analyze inbound and outbound emails to protect customers from spam, which represents 70% of globally mail sent

It can be annoying for the sender, but it saves the addressees from dangerous emails like malware and phishing. 


Types of Spam Filters 

There are three types of spam filters that can influence your deliverability. 

One is the gateway spam filter, which is a physical server installed at the border of a company’s network. It defends the mailbox of a company from spam and malware. 

Then we have third party spam filters, or hosted spam filters. They influence the filtering of emails according to the wide number of information they can use. They either send the email to the inbox, the spam folder, the quarantine or they can even decide to block the mail. 

Finally, there are desktop spam filters. They are a subsection of third party filters installed on the end user’s device. They can be set up with individual criteria, making it even more difficult to pass them and end up in the inbox. 


The technology and the analysis 

Spam filter technology uses algorithms and heuristics. They assign a numerical score to every element of the email that can be considered spam. 

Spam filters check a huge list of factors for every email. Among them, the most relevant are: 

  • the relationship between the sender and the addressee;
  • the reputation of your IP address and your domain; 
  • the quality and safety of the internal links; 
  • the quality of the subject line and the entire content of the email; 
  • the balance between text, links and images; 
  • the inclusion of a text version

They not only analyze these aspects, but they also track users actions to improve the future filtering

They consider if the user opened the email or not, if they scrolled to the bottom or if they read it and how much did it take to them. They also check if the user enabled images or flagged the email as spam and much more. 


How can you pass spam filters and avoid the spam folder?

Having an e-mail marketing campaign allows you to raise your ROI (Return on Investment). It gives you the chance to reach a wider audience, delivering relevant messages. 

Email marketing is a powerful tool for every business. To get the best results, you have to keep track of every performance. In this way, you will be able to see what is working and improve your strategy. 

To help you lower the chances of ending up in the spam folder of your subscribers, we gathered all the necessary tactics. 


1. Use the double opt-in 

The double opt-in can save you from both Spam-reports and bot accounts. They both can put your business in danger because they can damage the credibility of your brand and the deliverability of your emails. 

How does it work? 

First, you put an opt-in form in your website. Here users can add their emails and contact information. Then, you send them an email with a confirmation link. They have to click it to confirm they want to receive your content. 

In this way you will have the proof that they accepted to receive your emails when they will flag you content as spam. Furthermore, you can avoid bot subscribers that would harm your results and taint your KPIs. 


2. Give your content a balance  

One of the most important aspects of your email must be the balance between text, links and images

If you put too many images with no text spam filters will be triggered and will put your email into the junk folder. This happens because scammers and spammers usually use one or more big images that are difficult to read for filters. 

Another important aspect is connected to the links you insert inside your email. First of all, they have to be secure. Furthermore, you should prefer descriptive link text instead of URLs

Spam filters recognize URLs as phishing attacks, this is why you should never use them. 


3. Grow your list in an ethical way 

There are many different strategies that help you grow your mailing list. Yet, when it comes to this aspect you should remember to do it in a righteous way. 

You must never even think about buying an email list, since it is both forbidden in some countries and can damage your results. What you truly want and need are interested contacts. They are those that will be easy to educate and to turn into clients. 

You should never assume you have permission. Even if you have personal contacts and business cards, this doesn’t mean you have permission. You need proof. This is why you should always invite people to register to the newsletter using your (double) opt-in form. 


4. Build a relevant, spam-proof, subject line 

One of the key aspect of email marketing is the subject line. It influences not only the deliverability, but also the open rate of your email. 

To do that you have to craft a relevant and quality subject line. It has to engage the users and tell them what your email is about. 

If your subject line has no relevance with the email content, people will start to flag your emails as spam. 

Remember to avoid ALL CAPS sentences, the abuse of exclamation points and the use of different colors to make your text showy. 

Of course, you should also avoid spammy phraseology

The same goes for the entire text of the email. 

5. Use personalization 

As we said before, spam filters analyze the relationship between the sender and the addressee. This is why you should always personalize your email as much as possible

To do that you can add the recipient’s name in the subject line and in the first sentence. And you can also add other personal information inside the email thanks to the auto-fill options of email automation services. 

Personalization of email is also the best way to establish a relationship with your users. In this way they learn to trust you and to expect your content. This means that it will be then easier to convert them into customers.


6. Include a real reply-to address 

One of the worst decision of a brand could take is to use a non-reply address to send emails. 

Giving the opportunity to your users to establish a two-way communication is important to make them trust you. Using a non-reply address will make them feel as you don’t care about them. This can multiply the chances of having your emails flagged as spam. 


7. Don’t wait too long before you get in contact with your subscribers

To reduce the possibilities of your emails flagged as spam you should always remember to get in touch with your subscribers as soon as possible. Don’t wait to have a huge list of contacts, otherwise the first subscribers won’t remember you and will feel likely to tag you as spam. 

To help you do that, think about setting automation campaigns with the most relevant information for your users. 


8. Establish a consistent frequency 

What we said in the paragraph before is also true for the frequency of emails. 

In fact, if you don’t want people to forget you, you should send email with a consistent frequency

Be aware, though, that this doesn’t mean you have to be too pushy. If you start sending emails every day, people will get annoyed and will decide to unsubscribe or tag you as spam. 


9. Use the corporate email and not sketchy domains

Spam filters always analyze your domain. This is why it’s better to create and use a corporate email than personal ones. In this way your email will be more likely to pass the spam test and end up in the inbox.

Sketchy domains to avoid? Yahoo! and AOL are among the worst ones.

To improve even more the spam pass chances you should always use a reputable email service. In this way it will be more difficult to see your email pushed to the spam folder. 


10. Make unsubscribing easy 

The unsubscribe option is sacred and must be included in ever mail you send. In this way people will have the chance to stop receiving your communication without flagging you as spam. 

This is very important for your email marketing strategy because everytime a users flag you as spam your results keep getting worse. 


11. Include a text version of your email.

Having a text version of your email is good for more than one reason. 

First, it makes the spam-test easier to pass because spammer can use HTML to hide suspicious CTAs (Call To Action). Second, it makes the email easy to read even for clients using outdated email services. 



Email marketing is the most powerful marketing tool for every brand and professional. It allows you to improve your business results by engaging and educating a wider audience. In this way you can establish long-lasting relationships with potential clients. This means that you will be able to improve the conversion rate and the revenues thanks to a customer lifecycle focus. 

To get the best out of your email marketing campaign, you need a relevant and interested mailing list, and a strong strategy to pass spam filters

In this article we shared everything you need to know about spam filters and techniques to win them.

With uDroppy, you are always given the resources you need to improve your business results. Whether they are quality products, international shipping, personal support of an e-com manager, or marketing strategies. 

We do our best to give you the freedom and the power to reach the outstanding results you are looking for. 

Want to become a key player of e-commerce? Start working with uDroppy, the truly fully-integrated complete partner for your business. 

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