Resend event: email.complained, spam complaint, unsubscribe immediately

TL;DR

Check your suppression list: Resend adds complained addresses automatically.

Steps

1. Unsubscribe the address immediately, everywhere, not just the list that sent it. Never email them again without explicit re-consent.
2. Check your suppression list: Resend adds complained addresses automatically. Do not remove them.
3. Review what you sent: was it expected? Was unsubscribing hard to find? Did you mail someone who never opted in? A complaint is a content and consent problem, not a technical one.
4. Watch your complaint rate. Providers start filtering you aggressively well before you think the rate is high.

When to use

You are seeing this: The email was successfully delivered, but the recipient marked it as spam. Use this skill when you run into "Resend event: email.complained, spam complaint, unsubscribe immediately".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Resend's event reference says email.complained occurs whenever the email was successfully delivered, but the recipient marked it as spam. Verified live at https://resend.com/docs/webhooks/event-types. Suppression-list automation after a spam complaint is documented at https://resend.com/docs/webhooks/event-types.