Errors

All error responses share a consistent envelope. The HTTP status code matches the error type.

Last updated April 19, 2026

Error envelope

{
  "error": {
    "type": "validation_error",
    "message": "At least one of html or text is required.",
    "request_id": "req_abc123",
    "details": [
      { "field": "", "message": "At least one of html or text is required." }
    ]
  }
}

The details array is present only on validation errors and contains per-field messages. The retry_after field is present only on rate limit errors and contains the number of seconds to wait.

Error types

Type	Status	Description
validation_error	422	Invalid request body or parameters.
authentication_error	401	Missing or invalid API key.
authorization_error	403	Key lacks required scope.
quota_exceeded	403	Plan quota exceeded (mailboxes, sends, or team members).
not_found	404	Resource does not exist.
conflict	409	Idempotency key reused with different body.
rate_limit_error	429	Rate limit exceeded, or sending limit reached (daily ramp-up, per-mailbox, or throttle).
internal_error	500	Unexpected server error.

Quota exceeded error

A 403 response with type quota_exceeded is returned when a plan limit is reached. The message includes the current usage and limit.

{
  "error": {
    "type": "quota_exceeded",
    "message": "Mailbox limit reached (3/3). Your Solo plan includes 3 mailboxes.",
    "request_id": "req_abc123"
  }
}

See Plan limits for quotas by plan.

Rate limit error

A 429 response includes a Retry-After header and a retry_after field in the error body:

{
  "error": {
    "type": "rate_limit_error",
    "message": "Rate limit exceeded. Try again later.",
    "request_id": "req_abc123",
    "retry_after": 12
  }
}