How can I prevent my emails being blocked or sent straight to spam?

There are many reasons why emails end up in spam or are blocked altogether and thus do not reach the recipient as hoped. Having worked at the CSA for nine years, I can tell you that many senders still fail to implement the basic principles of successful Email Marketing. While the email world has been talking about features such as BIMI, AMP or schema for the past few years, there is actually still a lack of basic measures such as email authentication, an understanding that email addresses should not be bought or the ability for recipients to unsubscribe.

Listening and trust play the biggest role in email marketing, as in any good (sender and receiver) relationship. Listening means that the sender understands and responds to the needs and interests of its recipients. It also means paying attention to and responding to feedback from mailbox providers.

Trust refers to both the trust that the mailbox provider or spam filter provider has in the sender of an email and the trust that the recipient has in the brand, i.e. the sender of an email that is visible to them.

The task of mailbox providers is to ensure that all wanted emails get into the user’s mailbox and that unwanted emails stay out. According to Marcel Becker (Director Products at Yahoo), more than 90% of all emails are unwanted and are blocked on an MTA basis. The biggest challenge is separating the good from the bad.

And this is where trust comes into play. In terms of deliverability, the trust in a sender’s and their reputation are closely linked and both play an essential role. Reputation is built over time through a sender’s behaviour. Mailbox providers evaluate the reputation of senders to decide whether to move emails to the inbox or to the spam folder. Both are based on past experience. Trust ensures a good reputation for the sender, which in turn can be seen as a measure of the quality of the relationship between sender and recipient. If the mailbox provider trusts the email, they will let it through and it will end up in the inbox. If the recipient trusts the email, they will actually read the message and, ideally, perform the desired action.

So what are the key factors in building trust and improving reputation so that emails are more likely to be delivered to inboxes?

(In this blog post, I have only touched on the topics superficially to give you an overview. However, for a more comprehensive and detailed understanding, I recommend that you access our internal sources that I have provided on these topics).

1. Email authentication (SPF, DKIM, Domain Alignment, DMARC)

Email authentication is an important part of building trust. It allows the recipient to verify the authenticity of an email and ensure that it comes from a trusted source. Authentication allows the sender of an email to prove that they are indeed the person or organisation they claim to be. This ensures that the identity has not been stolen by third parties and the brand misused. Spoofing, phishing and other attacks can severely damage trust in a brand or company. Therefore, valid email authentication is essential to gain and maintain the trust of recipients. Email authentication therefore helps to create trust in email communication and protects both the sender and the recipient.

There are several email authentication mechanisms that work together to ensure the integrity and authenticity of emails:

SPF (Sender Policy Framework) defines which servers are allowed to send emails for a specific domain. This prevents unauthorised servers from sending emails on behalf of the domain.

DKIM (DomainKeys Identified Mail) adds digital signatures to ensure the integrity of the message. This allows the recipient to check whether the email has remained unchanged during transmission. See also DKIM Alignment.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) combines both of these mechanisms and defines how to deal with emails that do not meet the authentication requirements. It also enables monitoring and reporting on email delivery and authentication.

See our white papers and blog articles on email authentication.

DKIM beyond authentication – Protecting Brand identity and reputation

DKIM setup the easy way

DKIM Recommendations 2018 with consideration of the DKIM Crypto Update

DMARC and Domain Alignment in Email Marketing

Protect your brand from phishing emails by implementing DMARC

My DMARC Challenge – the Right Decisions and Their Ramifications

2. List building and maintenance, segmentation

The quality of a distribution list is very important. A high-quality and very well-maintained distribution list prevents spam complaints and thus has a great influence on reputation and deliverability. Unfortunately, many senders underestimate this fact. However, it is important to keep the following points in mind to avoid complaints about spam:

Consent: Send only to people who are genuinely interested in your content and have given their explicit consent. A reliable and legally compliant method of confirming this consent is the double opt-in (DOI) process. Also, let your recipients know what kind of emails they can expect, how often they will be sent and what they will look like. Adhering to the above points not only increases the chances of a positive response (engagement), but also minimises the risk of complaints about unsolicited or perceived spam emails.

Automation: An automated welcome email after registration is useful as it shows subscribers that registration was successful and that they are part of the distribution list (builds trust and avoids potential uncertainty.)

Segmentation: By segmenting your distribution list, you can divide your recipients into different groups and send targeted messages to specific target groups. Consider demographic characteristics, interests, buying behaviour or any other relevant criteria. Segmentation allows you to deliver relevant content, increasing the chances of engagement while minimising the risk of spam complaints.

Unsubscribe: Provide an easy way to unsubscribe. A prominently displayed unsubscribe button and one-click unsubscribe will prevent your emails from being marked as spam. This feature allows recipients to unsubscribe with one click, without having to go through any additional steps. In addition to the simple unsubscribe option, you should also offer the ability to customise email preferences. For example, some people may want to receive emails less frequently or only certain emails.

Read the following articles for more information:

List-Unsubscribe header

One-Click List-Unsubscribe Header

Why we should love our newsletter unsubscribers

3. Content & Engagement

It is important to regularly review the value of your emails and ensure that they are tailored to the needs and interests of your recipients. Invest time in creating relevant and engaging content that provides value to your recipients. This will increase the likelihood that your emails will be opened, read and even forwarded. Mailbox providers view these actions as a positive sign of the quality of your emails and consider you a trustworthy sender and your emails desirable.

4. Bounce Management

Monitoring and handling bounces is not given enough attention by many senders, yet it is an important issue for email deliverability. A bounce message is an automatically generated email sent by the mailbox provider to inform the sender that the original email could not be delivered. There are two types of bounces, depending on the cause: Soft bounces and hard bounces.

Soft bounces are considered temporary errors where re-delivery at a later date is recommended. In a soft bounce, the email could theoretically reach the recipient because the email address is correct. However, reasons such as the recipient’s mailbox being full or the receiving mail server being overloaded could temporarily prevent delivery.

Hard bounces are considered to be permanent errors and sending should not be attempted again. A hard bounce occurs, for example, when the email address is invalid or does not exist.

The distinction between soft and hard bounces is based on the status code returned by the receiving mail server. If the status code starts with “4”, it is a soft bounce, while a code starting with “5” indicates a hard bounce.

You can find more detailed information on this topic here.

5. Complaint management

Complaints will always occur and cannot be completely avoided even if quality standards are adhered to. However, how you deal with these complaints is crucial.

Complaints are valuable feedback and show you where there are problems and where there is room for improvement. There are a few points I would like to raise in relation to complaint management:

Abuse: You should set up a generic abuse email address in the format abuse@domain.tld (for example, to that abuse or spam reports can to be sent to you. It is important that you monitor this address and respond to requests. Note that mailbox providers may also communicate with you through this address to report problems or complaints. Overlooking or failing to respond to such messages can have a negative impact on your reputation and deliverability.

Complaint rate / spam clicks: A high complaint rate is one of the main reasons why emails end up in the spam folder. When users click on the spam button, this is recorded as a complaint by mailbox providers.  Too many spam clicks can reduce trust in your emails and damage your reputation. Lack of consent, lack of segmentation, lack of added value and lack of unsubscribe options are all factors that can lead to complaints and a high complaint rate. You can use a feedback loop (FBL) to get feedback on spam clicks.

(Feedback loop (FBL): “A feedback loop is a technical service provided by mailbox providers that reports spam clicks from email recipients back to the sender. This function is used when a recipient clicks on the “spam button” in the interface of their email account to complain about receiving an email from the mailbox provider”).

Read about it here.

Spamtraps: A spamtrap is a special email address that is not used by real people but is just bait. Its main purpose is to identify unsolicited spam emails and their senders. Spamtraps are used to improve the quality of email delivery and make spam filters more effective.

If someone sends an email to a spamtrap address, it is taken as an indication that the sender is sending spam If you follow the list hygiene points above, you will avoid hitting spam traps.

Read here what you can do if you still hit a spamtrap.


To be prepared for the future, it is important to do your homework and build a good relationship with your recipients. The basics of email marketing should be observed, because even features like BIMI are built on these fundamentals. People often talk about best practices, which sometimes sounds like an optional recommendation or is seen as a nice extra. But in reality, they are not just an option, they are a must for successful email marketing. Therefore, we should focus on implementing these best practices and consider them an indispensable part of our strategy. By mastering the basics and applying best practices, we lay the foundation for long-term success and a strong connection with our email recipients. Only through a good relationship built on trust can we deliver effective and successful email marketing in the long term.

N.B.: If you have followed all of the above and are still experiencing problems with the delivery of your emails, you can try to resolve the issue directly with your mailbox provider. Many large mailbox providers have so-called postmaster pages where they provide recommendations for senders and offer contact options if there are delivery problems.

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