Resend event: email.bounced, hard bounce, stop mailing that address now

# email.bounced: permanent rejection, remove the address

The recipient's mail server permanently rejected the email. This is a hard bounce. The address is invalid and will never accept mail.

## What to do on receipt

1. Remove the address from every mailing list immediately, and add it to your suppression handling. Never retry a hard bounce.
2. Record the bounce subtype if present: General (provider sent a hard bounce) or NoEmail (address does not exist or could not be determined). Both mean stop.
3. If this was a transactional email (receipt, password reset), surface the failure to the sender in your app so they can fix the address they typed.
4. Check your suppression list: Resend adds hard-bounced addresses automatically.

## The trap

Continuing to send to hard-bounced addresses. It destroys your sender reputation with providers, which hurts deliverability for your good addresses too. Also, do not confuse this with `email.delivery_delayed`: a soft bounce may resolve, a hard bounce never does. Resending to a bounced address is never the fix.