REST: POST /v1/messages

The canonical send endpoint. A drop-in for the SendGrid, Postmark, and SES REST shape: swap the base URL and the bearer, keep your code.

POST /v1/messages

Accepts a JSON message envelope. Returns a trace_id immediately and continues the routing decision + provider attempt asynchronously. The trace ID is public-shareable.

POST https://api.mailnix.ch/v1/messages
Authorization: Bearer mnx_live_…
Content-Type:  application/json

Request body

{
  "to":              ["jordan@acme.com"],
  "cc":              [],
  "bcc":             [],
  "from":            "noreply@example.com",
  "reply_to":        "support@example.com",
  "subject":         "Your receipt",
  "text":            "Plain-text body",
  "html":            "<p>HTML body</p>",
  "destination_id":  null,
  "template_id":     null,
  "template_vars":   {},
  "send_at":         null,
  "idempotency_key": "checkout-7c2d-receipt",
  "attachments": [
    {
      "filename":     "receipt.pdf",
      "content":      "<base64>",
      "content_type": "application/pdf"
    }
  ]
}

destination_id is optional; omit it and mailnix picks a destination from your routing rules. template_id + template_vars render a saved Sprig template server-side. send_at is an RFC3339 timestamp up to 3 days in the future (Pro+ only).

The outcome field

The response carries an outcome string that tells you exactly what mailnix did with the message:

relayed: sent to a real provider.
captured.anonymous_project: the project is anonymous; capture only.
captured.sandbox_destination: the matched destination is in sandbox mode.
captured.no_route: no routing rule matched; the project's no_route_policy was capture.

Idempotency

Pass an idempotency_key on retry-prone callers (checkout, signup, webhook worker). mailnix indexes the key per project for 24 hours; a duplicate POST returns the original trace ID instead of producing a second send.

Scheduled sends

Set send_at to an RFC3339 timestamp in the future (max 3 days, Pro+). The response carries the same shape but with status: "queued"; the actual provider attempt happens at send_at. Cancel via DELETE /v1/messages/scheduled/<trace_id>.

Errors

Every error has the same envelope shape:

{
  "error": {
    "code":        "validation_failed",
    "message":     "from address is missing",
    "next_action": "supply a verified sender or set destination_id"
  }
}

Common codes: validation_failed, quota_exceeded, quota_exhausted_captures (HTTP 402), destination_misconfigured, provider_rate_limited, insufficient_scope.