Event Reference

Each webhook request is a JSON list of events. Every event has the same shape; data.details holds what's specific to the event type.

Event types

Type	Sent when
delivered	The recipient's mail server accepted the email. This doesn't mean it reached the inbox; the server may still file it as spam.
deferred	The recipient's server temporarily refused the email. SendMero keeps trying, so a delivered, bounced or expired event usually follows.
bounced	The recipient's server permanently refused the email.
expired	SendMero stopped trying after the email was deferred for too long.
complained	The recipient marked the email as spam, where their mailbox provider reports this.
rejected	SendMero accepted the request but couldn't send the email, for example because the API key was revoked or the sending domain isn't ready. details.reason says why.
suppressed	Coming soon. The email wasn't sent because the recipient is on your suppression list.
unsubscribed	The recipient unsubscribed through an unsubscribe link. details.unsubscribe.scope is group (one of your unsubscribe groups, or the sending domain's own group) or workspace (all your mail), and details.unsubscribe.group names the group.
resubscribed	An unsubscribe was removed, because the recipient switched a group back on or resubscribed, or because you removed the entry in the dashboard. details.resubscribe.scope and details.resubscribe.group say which unsubscribe it was.

When you choose All events, new types are included automatically, so ignore types your code doesn't know.

Fields

Field	Type	Meaning
id	string	Unique event ID (evt_…). Use it to ignore duplicates.
type	string	One of the types above.
created_at	string	When SendMero recorded the event (ISO 8601, UTC).
test	boolean	Only present, as true, on events from the Test button.
data.message_id	string	The id returned when you sent the email (msg_…).
data.recipient	string or null	The recipient this event is about.
data.domain	string or null	Your sending domain.
data.occurred_at	string	When it happened (ISO 8601, UTC). Use this to order events.
data.attempt	number	The delivery attempt this event came from.
data.metadata	object	The metadata you sent with the email, or {}.
data.details	object	Details for this event type, described below. May be {}.

details

details.smtp

Included when the recipient's mail server replied.

Field	Type	Meaning
code	number or null	SMTP status code, for example 250 or 550.
enhanced_code	string or null	Enhanced status code, for example 5.7.1.
response	string or null	The server's reply text.
remote_ip	string or null	The address of the server that replied.

details.bounce

Included on bounced and expired events (expired is always soft).

Field	Type	Meaning
type	string	hard (the address won't work, stop sending to it), soft (a temporary problem that lasted too long), block (refused because of the sender or content, for example reputation) or admin (refused by a policy).
classification	string or null	A more specific reason, when known.

details.reason

A short machine-readable reason, on events that have one but no bounce, such as rejected (for example domain_not_ready:…).

Example: delivered

[
  {
    "id": "evt_8d2f0c1e5b7a4f6d9e3c2b1a0f9e8d7c",
    "type": "delivered",
    "created_at": "2026-09-25T10:00:04.512Z",
    "data": {
      "message_id": "msg_fb8076ffc18c225d4fa617f8b00ed038",
      "recipient": "someone@example.com",
      "domain": "mail.yourdomain.com",
      "occurred_at": "2026-09-25T10:00:03.981Z",
      "attempt": 1,
      "metadata": { "order_id": "88231" },
      "details": {
        "smtp": { "code": 250, "enhanced_code": "2.0.0", "response": "OK", "remote_ip": "142.250.27.26" }
      }
    }
  }
]

See Webhooks for setting up endpoints, retries and securing your endpoint.