While it may seem intimidating at first, overcoming spam filters and other deliverability issues isn't rocket science. With the right knowledge, you can reduce the chances of your emails getting caught by spam filters and achieve better deliverability rates.
Here, we'll demystify how spam filters work and how they assess whether an email is spam or not. We'll also explore the most critical factors that spam filtering algorithms take into account. Finally, we'll reveal the 10 most effective tricks to get your emails past even the strictest spam filters .
So, let’s roll up our sleeves and get your email deliverability up and running.
Why do emails end up in SPAM?
Let’s face it – everyone has been a victim of unsolicited emails and spam and wonders how to get rid of them. At best, they are simply annoying but harmless, littering your inbox with irrelevant ads and promotions. However, at worst, they can cause serious damage, leading to substantial financial and reputational losses. Through spam emails, criminals perform social engineering, spoofing, data theft and create all sorts of other problems.
To protect their customers from such malicious events, Internet Service Providers and Email Service Providers incorporate spam protection systems and spam filters to keep recipients and their networks spam-free . They act as gatekeepers of the recipient's inbox, subjecting incoming emails to rigorous and thorough checks before approving them. From the moment you send your email until it reaches the recipient, it passes through one or more filters with the goal of identifying and stopping malicious or unwanted messages. Each spam filter has its own set of rules, threshold, sensitivity, spam trigger words, etc. You can't anticipate and predict everything, but you can at least understand the most common reasons that trigger spam filters and minimize the chances of your emails ending up in spam folders.
How do spam filters work?
Spam filters use a complex set of rules, algorithms, and artificial intelligence to evaluate emails and set the spam score threshold . They put every incoming email message under the microscope to decide its fate. After the filters have gone through all the checks, they assign a spam score to the emails. If the emails meet the predefined threshold, they are given safe passage to the recipient’s inbox. However, if the score is higher, they may be kicked out to the spam folder; be completely rejected at the network level without any kind of response to the sending server; or drop outright with an error, something like a hard bounce .
Types of spam filters
In general, there are several different types of spam filters, which take different approaches to detecting spam.
Blacklists
These filters monitor different denylist/blacklist databases worldwide and will stop emails from IP addresses included in these blacklists. Denylists (blacklists) are databases containing lists of domains and server addresses that have been reported as frequent senders of spam content.
Content filters
Content filters review the email message and look for specific words and language that might suggest the email is clickbait, phishing, or another type of spam. Most content filters look for similar things: profanity used multiple times, such as “deals,” “limited time,” sexual language, and others. They also watch out for common scams like the “419 scam,” most famously when someone impersonates a Nigerian prince who asks for money in exchange for the promise of repaying a larger sum in the future.
Header Filters
These filters focus on reading information transmitted through the email header, such as the originating IP, whether the email is being sent to a group of recipients, and more, and aim to ban messages from bad sources, such as IPs used by spammers.
Language filters
Some email service providers monitor the language of emails and if that language denmark whatsapp number data differs from the language of the recipient's country, they may stop the messages. These filters can be configured differently, but generally aim to protect recipients from content that is not tailored to their needs.
Email service providers and users can use a filter to set up specific rules that can be applied to all incoming emails. For example, you can set the filter to stop all emails from a specific sender, or search for specific words or phrases in the body or header of incoming emails and if detected, the message is sent to the spam folder.
Bayesian filter
Bayesian filters monitor recipient preferences by examining the emails they send to spam and set rules based on the patterns they detect to automatically flag similar emails in the future.
AI Filters
AI is increasingly being used to combat spam. Its purpose again is to detect patterns in emails, sender behavior, and more to help spam filters more accurately flag messages passing through the network. AI is trained on real content coming in and out of the network, using real messages to learn what is good and what is bad, and its contribution to this fight is becoming increasingly valuable.
How do spam filters calculate the Spam Score?
Email service providers constantly update the rules their spam filters use in response to the ever-changing and clever ways spammers find to catch email users off guard. But still, there are some essential elements and common criteria that all spam filters take into account when forming the spam score for your emails.
Sender reputation
The first thing spam filters do is check the sender reputation. As we discussed in detail in our article on email deliverability, this refers to the credibility of your sender IP. If your IP appears on any blacklists/denied lists, your emails will be marked as spam.
Domain Reputation
Let's say your IP is clean, but your domain has a negative history and is known for sending spam. Again, this information may be recorded in public denylists or private databases of the recipient's email provider. Unlike sender reputation, where the responsibility is shared with your PES, domain reputation is something you are personally responsible for, and you should monitor it carefully.
Quality of email content
Email content quality is critical to both user engagement and avoiding the spam filter. High-quality content is relevant, well-written, and provides value to the recipient. When creating email campaigns, email marketers should learn to avoid “ spam trigger words ” – specific words or phrases that can set off spam filters. You don’t have to think about it too much, but as a general rule, these words are often associated with deceptive or aggressive marketing practices. Remember the Nigerian prince and the content filters above? Just like those.
The quality of the content served greatly affects user engagement with your emails . High user engagement is a positive signal to email providers that recipients value your content and that you're not spamming. And vice versa. You can easily monitor that engagement with several metrics — open rates, click rates, replies and forwards — and aim to improve the quality of your emails with each campaign.
