What is a spam email filter?

Unwanted emails are commonly known as spam and out of the billions of emails which are sent each day, over half are spam or unwanted emails.

Email filters are programs or algorithms which are used at various levels of an email's delivery to your inbox such. This can include the email service such as hosted email and Microsoft Exchange or the email software you use to access email such as Microsoft Outlook or Apple Mail.

The filter's which are used run protocols which focus on various items that form an email. These include:

Email Header

An email header is an item of code which appears before the content within an email. It contains information about the sender and the recipient which is essential to conform that the email is authentic.

Falsified email headers provide confirmation that the email is spam as a spam email will contain an email header with false information which prevents any recipient from responding to or tracking their location.

Content Filter

A content filter will check through the body or content of an email to find words or items which may be identified as spam. Filters can compare it to the current emails within the inbox as well as the current messages which are marked as spam.

User Defined Filter

User defined filters work by individual users reporting spam emails to a central database or service which identifies spam emails and newsletters.

Blacklisted Addresses

A blacklisted address filter blocks emails which have been added to a spam list and are continually updated when different email addresses are identified from the same sender.

User Permission

Email recipients are able to create filters which will only allow emails to appear in their inbox from a set list of senders.

Avoiding The Spam Folder

There are a number of actions you can implement with your email setup along with some simple factors to consider when creating your email content and subscriptions which increase your deliverability to a users' inbox

Send Emails From Your Domain

Using email services such as Gmail, Outlook or Yahoo to send individual, single emails are fine and should not encounter any spam or delivery issues. However, when sending bulk emails such as a newsletter to a large number of recipients, it is always best to send the email from your own domain.

Search engines are used by email algorithms and software to determine genuine domains for websites which appear in the search results aiding towards the verification of your identity when sending bulk emails. So if an email client is unable to determine the identity of a domain owner, they may mark the email as spam.

Use Clear Email Addresses Which Don't Change

If you use a clear, generic email address such as noreply@, newsletter@ or update@ when sending bulk emails to your recipients, email clients and spam protection programs will recognise the email address as a trusted sender.

There are no issues with personalising your email address with your name such as john@ or sarah@ as long as you don't use an email address which frequently changes or use odd names like qwerty123@, the emails which are being sent will have a high risk of being marked as spam.

Manage Your IP Reputation

An IP address is a string of numbers which identifies your server and location. With your email hosting, you will either be using a shared IP address, which will be used by other email users or a dedicated IP which will only be used by yourself.

The benefit of using a dedicated IP address is that there will only be yourself using it for your email along with any other services such as website hosting and storage, allowing you to fully manage your IP reputation.

Spam Trigger Words & Phrases

When sending out emails as part of an update to customers or a marketing campaign, it's easy to use hard sell words and phrases like Buy Now and Save Big which can indicate that an email is spam.

When creating content for your emails, try to avoid using content which can be seen as desperate, pushy or too good to be true.


By default, many email clients will not show images unless they have been instructed to do so by the user so it is important to provide the information to users in a text format.

However, when images are used, having a high ratio of text to images will increase the deliverability of your email. If your email contains just images or a large number of images and small amount of text, it may be marked as spam by an email client or protection software as it is widely known that spammers will use images, so that the spam content cannot be read.

Link Quality

It is important to check the links which are being sent within an email. Any links with a poor reputation which you send will in turn, flag your own IP address with a potential poor reputation by association.

Some of the actions you can take to ensure that the link quality is high within your emails is to not use link shorteners such as bit.ly and to only link to your own website where you can then provide further information, links and resources to subscribers.


Double Opt-In

Having a double opt-in setup for users to subscribe to any email newsletters or updates will ask users to confirm their subscription by email after they have provided their initial details and email address.

Although a double opt-in is not required under GDPR, it will reduce the risk of emailing spam email addresses, provide proof that subscribers are genuinely interested in receiving updates which will improve your overall reputation and deliverability of your emails to the inbox.


Email Send Tests

If emails are tested before sending them to your active subscribers, the email experience can be tested and checked over for deliverability, readability and layout.

Provide Subscription Options

Even though it is not great to lose email subscribers, it's important to provide users with the option to unsubscribe. If users are unable to unsubscribe, they will simply mark any emails as spam.

Expanding the subscription options to users so that they are able to choose the types of emails they will receive will be an advantage along with options to provide feedback for users to explain why they want to unsubscribe, in turn helping to improve any email marketing.

Consider The Subject Line

As well as being a crucial element in engaging with users to ensure a high open rate, the subject line should avoid using all caps, should be short, relevant to the email content and avoid any words or phrases which are desperate, pushy or too good to be true.


For the most part, monitoring, managing and finding ways to improve the quality of the emails and the subscriber list will mean most email spam filters will be avoided, emails will be prevented from ending up in the spam folder and the IP address or domain reputation will continue to be trusted.

Learn More

If you would like to speak with the Digital Chimps to discuss your email marketing or email services, please get in touch using the following details.