email.bounced

Fires when the mail provider reports that a message sent from a connected mailbox bounced. The message is marked as bounced in Custral as the event fires.

Not every bounce is detected. This event depends on the mail provider’s bounce report being recognised, and some are missed: rejections from another domain’s server, reports in a language other than English, and connection failures. Do not rely on it as your only signal that an address is bad, and treat an email.bounced delivery as confirmation rather than as the complete list.

Payload

{
  "id": "whd_6Qe2tJ8vH",
  "event": "email.bounced",
  "createdAt": "2026-09-11T12:20:14.036Z",
  "data": {
    "messageId": "18f2d3e7a9b1c4f6",
    "recipient": "ada@ravennafoods.com"
  }
}

string

required

The mail provider’s id for the message that bounced. Always present.

string

The first address the message was sent to. An empty string when that could not be read.

Worth knowing

Only the first recipient is named. For a message sent to several people, recipient is the first to address, which may not be the one that bounced.
Nothing is suppressed. A bounce marks the message and leaves future sends to the address alone. Suppress it yourself if you need to.

Example

custral.on("email.bounced", async (event) => {
  const {messageId, recipient} = event.data;
  if (!recipient) return;

  await deliverability.flag({address: String(recipient), messageId});
});

Getting started

Building a receiver

Event reference

Operations

Payload

Worth knowing

Example

​Payload

​Worth knowing

​Example

Payload

Worth knowing

Example