Reference

Limits & errors

Rate limit

10 requests per second per API key. Over the limit you get 429 with Retry-After: 1.

Quotas

Monthly and daily email quotas depend on your plan. Exceeding them returns 429 monthly_quota_exceeded or daily_quota_exceeded.

Error format

{
  "statusCode": 422,
  "name": "validation_error",
  "message": "Missing `to` field."
}