Complaint (feedback loop)
A complaint is what happens when a reader presses the spam button. Large mailbox providers report those presses back to the sender over a feedback loop, so you learn which address complained even though the reader never wrote to you. Complaints are the strongest deliverability signal there is, and a rising rate costs you the inbox for everyone else on the list.
At a glance
- Category
- Deliverability
- Triggered by
- A reader marking a message as spam
- Reported over
- A feedback loop, from the mailbox provider to the sender
- Arrives as
- An event naming the address and the message
- Correct response
- Suppress the address immediately, every time
How it works
A reader opens a message and presses the button their client calls spam or junk. Their mailbox provider records that verdict, and for senders enrolled in its feedback loop it sends a copy of the complaint back. Your sending service turns that into an event naming the message and the address. Some providers redact the recipient, which is why the message identifier matters more than the address in the report. The reader is told nothing, and from their point of view the conversation is simply over.
Why it matters
Nothing you can measure is closer to the question a mailbox provider is actually asking, which is whether their users want your mail. Opens can be faked by a proxy and clicks can be accidental, but a complaint is a person deliberately saying no. Because providers aggregate complaints by sending domain, one campaign to a stale list can move the verdict for every message that domain sends afterwards, including the ones people are waiting for.
Example
A newsletter goes to a list that has not been mailed in fourteen months. Several hundred readers no longer recognise the sender and press the spam button rather than hunt for an unsubscribe link. Each press arrives as a complaint event, and each of those addresses is suppressed at once. The damage is not the lost recipients; it is that the next campaign from that domain starts from a worse position with every provider that saw the spike.
Common mistakes
- 01Treating a complaint as a bounce and retrying, which turns one refusal into a pattern the provider can see.
- 02Hiding the unsubscribe link to keep the list large, which converts unsubscribes into complaints and makes the outcome far worse.
- 03Watching only the total rather than the rate per provider, so a problem at one mailbox provider is averaged away by good numbers elsewhere.
In Rasket
A complaint suppresses the address immediately and arrives on your webhook endpoints as an email.complained event. Events
Related terms
Frequently asked questions
Can I contact someone who complained?
No, and you should not try. The correct response is to stop sending to that address entirely, which is what suppression does automatically.
Why does the complaint not always name the address?
Some providers redact the recipient before forwarding the report, for the reader's privacy. The message identifier is still there, and that is enough to find the address in your own records.
Do all mailbox providers run a feedback loop?
No. Several large ones do, some offer aggregate reporting instead, and others report nothing at all. That is why complaint rate is always a partial picture of how readers feel.
Last updated 16 September 2026.
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