Permanent (5xx)
SES: Complaint (feedback loop)
Recipient marked the message as spam
Not a bounce at all - the recipient's mailbox provider reported back (via a feedback loop) that the recipient clicked "mark as spam."
Common causes
- Recipient didn't recognize the sender or didn't expect the email.
- Missing or hard-to-find unsubscribe/opt-out on non-transactional content.
What to do
- →Suppress the address immediately - continuing to send after a complaint damages sender reputation for every other recipient too.
- →Make sure transactional email is actually transactional (triggered by the recipient's own action), not disguised marketing.