CSA, how did your criteria actually come about?
Part I: The Spam Marking Rate

A series of articles on the background to individual CSA criteria

The relationship between mailbox providers and the CSA

We know: The CSA criteria are strict. Sometimes, corporate IT resources and an adjustment of the sending infrastructure or sending strategy are required to meet the criteria for successful certification. Is it worth it?

Spoiler: Oh yes, it is. Especially in the long term for your own reputation. Because, depending on the business model, reputation is the basis for one’s own business model and this ultimately also has a positive effect on ROI.

In order to explain why the criteria exist in the form they do, who specifies them, and what advantages they bring with them, we will examine a few of our criteria by way of example in this series of articles. Specifically: In this article we will look at the spam mark rate (criterion 2.22). The limit for this is 0.3% (link criteria).

Let’s talk about the title of the article: The CSA didn’t just write up the criteria on a whim. The criteria reflect what mailbox providers expect. And here the interaction of mailbox or spam filter providers and the CSA becomes clear. The CSA transports the expectations and standards of the mailbox providers. Compliance with their standards (via the criteria) is then rewarded, among other things, with better deliverability.

The spam marking rate at the CSA

A brief explanation: The Spam Mark Rate (also Spam Complaints Rate) shows how many recipients have complained about a received message, i.e., flagged it as spam. An example calculation could look like this: If a mailbox provider receives 30,000 mails from a sender and 60 recipients mark the mail as spam, then the spam marking rate is 0.2% – the CSA looks at the 7-day average – which would even allow for individual outliers towards the top.

We are often asked why we are so strict with this value, since as a sender you can already exceed it with just one campaign that only touches on the target group or that was sent to an old mailing list. Here we come to the real issue: This is because this value is not something that the CSA makes up, but is rather a response to the mechanisms of the mailbox providers. These are based in part on much stricter values, which in part already apply at 0.1 % or below. If a sender is constantly above this level, the mails from this sender will be treated as spam by the internal (learning) mailbox filter.

Improving this situation can only be achieved with targeted measures and the consistent application of best practices. The reduction of spam complaints then leads to a recovery of reputation in the long run.

What can I do about a high complaint rate?

The following tips can help against a high complaint rate:

  • Set the right expectations at the time of registration and maintain them towards the recipients in the long term.
  • Use captchas and, even more importantly, the double opt-in procedure. This ensures that you do not generate any bot traffic.
  • Show clear and valuable added value to the recipient when signing up to an email list.
  • Users connect the domains of websites, their content, and the context of the login. Emails from unknown, deviating domains are increasingly perceived as spam.
  • Only send to contacts that have opened in the last period of time (e.g. the last 3 or 6 months).
  • Only send to contacts that have registered in the last time (max. 2 years) have registered.
  • To ensure that a subscriber also remembers that they have given an opt-in, do not wait too long between registration and the sending of the first mail and point out in the mail why the recipient has received it.
  • Only send relevant campaigns to the target group that meet the set expectation of the sign-up and offer real added value.
  • The CSA offers certified senders data from mailbox providers for their own reputation management.
  • If a recipient complains about an unsolicited email from a Certified Sender, the eco Complaints Office will inform the sender for its own protection.


The spam mark rate is an important CSA reputation factor, also at the CSA. If this is permanently too high, the reputation of a sender suffers.

The CSA’s goal is to optimise and protect the reputation of certified mailers. Therefore, the CSA provides certified senders with data from the mailbox provider’s point of view to monitor their own performance.

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