Spam filters

7 tips to prevent getting blocked by spam filters

Ever since the early days of email marketing, spammers have tried to invade our inboxes. To protect ourselves against this nuisance, we invented spam filters. But that brought along another issue, especially for us email marketeers, as protection sometimes leads to overprotection. In other words: what can we do to get our legitimate content through those rigorous spam filters?

Let’s see how spam filters work

Spam filters use 3 different levels to assess an incoming email. After looking into each factor individually, the spam filter determines if an email will pass through the filter. 

  1. First your message needs to pass the spam filter of the ISP (internet service provider).
  2. The next hurdle to take are the spam filters installed by companies (some of your B2B clients may have very strict filters in place).
  3. Once you have reached your contact's email client, it can still be labeled as ‘unwanted’.
Spam filters work according to certain criteria and use a list of known spam related situations. Based on this information, the filters will decide whether your message is tagged as spam or not. Want to know what spam messages look like – and how to make sure your own emails don’t end up in their league?

Here are 7 ways to make sure your email don’t get stuck in spam filters.

1. Authenticate your emails

A good way to make spam filters recognise your emails as legitimate messages is to authenticate them. By configuring email authentication, you activate a process that verifies the identity of the sending server before your email is delivered to your contacts’ inboxes. This guarantees that no one can ‘steal’ your identity to falsely send emails in your company’s name. 

Do you want to dive deeper into this topic? Check out this blogpost: How to improve your email deliverability.

2. Mind the reputation of the IP address you send from

So important: make sure you send your emails from a server with a good reputation. This is based on past behavior, combined with a reliable identity. IP addresses of email marketing platforms such as EMG+, Hubspot, Mailchimp, etc. perform well in this field. 

Prefer to use your own email server? By all means check its reputation score on Your server’s score is calculated based on the following evaluation points (3-7). 

3. Check how your readers treat your emails

Spam filters can trace how your readers deal with your emails. If they consistently delete them without even opening them, your reputation score will inevitably go down.

4. Prevent people from reporting your emails as spam

The more people mark your emails as spam, the more likely spam filter will see them as such. The answer: send your emails to people who actually signed up for them and are interested in reading your content.

BONUS TIP: don’t use bought or rented lists
You can legally purchase lists of people who have agreed to receive email communication. But be aware that this doesn’t mean they automatically agreed to get your emails, increasing the chance they’ll label them as spam.

5. Keep your database clean

Spam filters keep track of how many emails you send to non-existing addresses. Those so-called hard bounces have an immediate and negative impact on your reputation score. Monitor your database on a regular basis and clean out bounces and non-responsive email addresses.

6. Strip spam sensitive content from your email

A few years ago, certain individual words — viagra, free, win, … — used to trigger spam alerts. Nowadays, spam filters are more inclined to respond to certain patterns. 

Some of the most common spam-flaggers, to be avoided at all costs: 

  • Unbalanced text-image ratio: image-only mails are suspicious. Even too many or too large images compared to the text areas in an html email tend to look spammy. Add text or reduce image use in order to keep the balance.
  • Exaggerated (!!!!) use of exclamation marks 
  • USE OF CAPS ONLY in text (especially in subject lines)
  • Excessive use of different colors and font types
  • Illegitimate use of ‘RE’ or ‘FW’ in subject lines to suggest previous conversation
  • Spammy words and phrases in your emails’ subject lines or body copy, such as “buy direct”, “Don’t delete”, “Do it today”, “Earn extra cash”, …
  • d0ing w3ird th1ngs with letters and numbers

7. Use the correct html coding

Nobody likes sloppy html code, superfluous tags or code pulled in from Microsoft Word. Spam filters immediately respond to coding errors and your recipients’ email clients could have difficulty displaying your emails correctly.

 Make sure your code is simple and well-structured. When in doubt, check your html via tools like


Spam filters are useful, but they can be a nuisance for legitimate email marketers like us. By following the above set of basic rules, you can significantly reduce the risk of getting you emails banned from your contacts’ inboxes. Need some extra advice or tips on this subject? Get in touch with RAAK: we’re here to help you.

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Posted on
Feb 17, 2021