Complaint Rate

Why is my email going to spam?

You know something is off when your messages stop arriving in inboxes. Numerous causes come to mind, like using a fake or incorrect email address or missing data. Chances are your email ended up in spam. This usually means you're dealing with an extravagant complaint rate. A complaint rate indicates the value of your transactional email flows. If your complaint rate gets a little too high, it has an immediate impact on your email deliverability. In our Flowmailer dashboard, we provide you with reports on this complaint rate. However, what exactly is a complaint rate, and how did you get this far?

In this article, we provide context on the concepts of 'Feedback loops', 'Complaints', and 'Complaint Rate'. Furthermore, it describes how these complaints develop and what measures you should take to fix them.

Feedback loops & complaints          

As your transactional emails reach your recipient's ISP, like Outlook, Gmail, or Yahoo, he or she gets the chance to define your message as 'unwanted'. This action results in sending it to spam or deleting the whole email.


Signals like these are sent back from the ISP to Flowmailer. We call it the feedback loop. With this loop, we ensure this recipient is not being sent email anymore by adding him to a filter list. On this filter list, he's given the status of 'complaint', so you know exactly what happened to this specific recipient.

Given the nature of the messages you're sending via our platform, it's unlikely that the amount of complaints is alarming. When complaints do happen to come in, you are the first to know. Flowmailer's dashboard visualizes the complaint rate. A complaint rate calculates all complaints per amount of sent emails in a given period. Flowmailer typically shows this for 'today'.

Why people mark you as spam

There are several motives for a recipient to mark your email as spam. Each reason requires a different approach. It goes without saying that when your email server fails to deliver, customers will take action themselves. However, even when your messages do arrive, they're complaining about your emails now and then. What moves these people?

The Golden Rule in complaint rates: Any rate above 0.03% is alarming. This rate requires immediate action.

Concerns for commercial follow up emails

The primary reason for recipients to send you to spam is their fear for commercial emails. Because chances are that, now that you've got their email address, the next step is to send them a promotional email, right? With this fear comes the inevitable click on 'Mark as spam'. You're basically done sending them anything from now on, even their future order confirmations or forgotten password-mails will stop arriving. If this happens, it is essential to take action on these kinds of complaints.

Customer service could help you out with this. Let them reach out to the recipient and comfort him. After that, ask him if he really never wants to get your email anymore. If so, you're out. If not, ask him to drag the email from spam back to the inbox. The ISP will know that the email is not unwanted anymore and will allow your future emails to land in the inbox again. Removing this recipient from the filter list is your next step.

You've over-commercialized your transactional email

As indispensable communication, transactional email is crucial to its recipient. Of course, transactional email leaves room for some commercial influence. However, if you exaggerate this, it will inherently influence the number of complaints. Try balancing out the service message versus commercial message at 80/20. Also, get your different types of messages to conform to each other. You will find that this rate (80/20) barely results in complaints.

Humans make mistakes (they do!)

Of course, your recipient could have hit 'spam' by accident. This kind of complaint usually doesn't result in a high complaint rate, since not everyone just accidentally does that. It is, though, essential to take action, as described before.


The complaint rate is a vital indicator of how your recipients experience your transactional emails. If your approach is too commercial, it will result in a higher complaint rate. This complaint rate requires immediate action to make sure your future emails will still get delivered. Check your complaint rate frequently on our platform (max. 0.03%)