Hello.
", "text_body": "Hello." } ``` Required fields: `from`, `to`, `subject`, `html_body`. Useful optional fields: - `text_body`: plain text alternative. - `cc`, `bcc`: arrays of recipients, max 100 each. - `reply_to`: one address object. - `return_path`: envelope sender for bounce handling. - `custom_headers`: custom `X-*` headers. - `attachments`: up to 10 items. Prefer uploaded refs `{ "attachment_id": "att_..." }`. Inline compatibility form uses `filename` plus base64 `content`, optional `type`, and `encoding: "base64"`. For real local files, do not ask the model to produce base64. Route attachment-heavy work to `sendmux-attachments`; use CLI `--attach`, SDK file helpers, `sending_upload_attachment`, or delegated `sending_create_attachment_upload`, then pass `attachment_id` refs. Sending uploads cap each file at 18 MiB and the final sent message at 25 MB. Mailbox `blob_id` refs are for mailbox sends, not Sending API sends. Batch send body: ```json { "messages": [ { "from": { "email": "sender@example.com" }, "to": { "email": "alice@example.com" }, "subject": "Hello Alice", "html_body": "Hi Alice.
" }, { "from": { "email": "sender@example.com" }, "to": { "email": "bob@example.com" }, "subject": "Hello Bob", "html_body": "Hi Bob.
" } ] } ``` ## Idempotency Add `Idempotency-Key` to every send that may be retried. Use one stable key per logical email or batch. - Same key and same body: returns the cached response for 24 hours. - Same key and different body: returns `409 idempotency_conflict`. - Keep keys under 255 characters. ## MCP Use MCP when the user's agent already has the Sending server connected: - One message: `sending_send_email`. - Multiple messages: `sending_send_email_batch`. - Local file upload before send: `sending_upload_attachment` with `file_path`. - Hosted or shell-capable upload before send: `sending_create_attachment_upload`, then `PUT` bytes to the returned URL with the returned headers and no Sendmux API key. - Metadata check for a temporary uploaded attachment: `sending_get_attachment`. Include an idempotency key when the client exposes the header parameter. If the MCP client does not expose headers clearly, use CLI, SDK, or direct HTTP for retry-sensitive sends. For attachments through MCP, use `sendmux-attachments` so the agent chooses `file_path`, presigned upload, or tiny inline base64 correctly. ## CLI One email: ```bash SENDMUX_API_KEY="$SENDMUX_MBX_KEY" sendmux sending:send \ --idempotency-key "$IDEMPOTENCY_KEY" \ --body '{ "from": { "email": "sender@example.com", "name": "Sender Name" }, "to": { "email": "recipient@example.com", "name": "Recipient Name" }, "subject": "Subject line", "html_body": "Hello.
", "text_body": "Hello." }' \ --json ``` Batch: ```bash SENDMUX_API_KEY="$SENDMUX_MBX_KEY" sendmux sending:send:batch \ --idempotency-key "$IDEMPOTENCY_KEY" \ --body-file ./sendmux-batch.json \ --json ``` Use `--attach ./file.pdf` for local files; the CLI uploads bytes first and injects `attachment_id` refs before sending. Use `--body-file` for larger JSON payloads or already-prepared Sending API attachment objects. ## TypeScript SDK One email: ```ts import { createSendingClient, sendingSendEmail } from "@sendmux/sending"; const client = createSendingClient({ apiKey: process.env.SENDMUX_API_KEY! }); const response = await sendingSendEmail({ client, headers: { "Idempotency-Key": idempotencyKey }, body: { from: { email: "sender@example.com", name: "Sender Name" }, to: { email: "recipient@example.com", name: "Recipient Name" }, subject: "Subject line", html_body: "Hello.
", text_body: "Hello.", }, }); console.log(response.data.message_id, response.data.status); ``` Batch: ```ts import { createSendingClient, sendingSendEmailBatch } from "@sendmux/sending"; const client = createSendingClient({ apiKey: process.env.SENDMUX_API_KEY! }); const response = await sendingSendEmailBatch({ client, headers: { "Idempotency-Key": idempotencyKey }, body: { messages, }, }); for (const result of response.data.results) { console.log(result.index, result.status, result.message_id, result.error); } ``` ## Direct HTTP Use direct HTTP only when MCP, CLI, or SDK is unavailable: ```bash curl -X POST https://smtp.sendmux.ai/api/v1/emails/send \ -H "Authorization: Bearer $SENDMUX_MBX_KEY" \ -H "Content-Type: application/json" \ -H "Idempotency-Key: $IDEMPOTENCY_KEY" \ -d @sendmux-email.json ``` ## Responses and errors Single send success returns a `200` success envelope with: - `data.message_id`: `eml_...` - `data.status`: `queued` Batch success returns a `200` success envelope with: - `data.summary.total` - `data.summary.queued` - `data.summary.failed` - `data.results[]` containing `index`, `status`, `message_id`, and optional `error` Handle these errors deliberately: - `401`: missing, invalid, or revoked key. - `402`: insufficient credits. - `403`: key lacks `email.send`, is not allowed for the sender, or uses the wrong surface. - `409`: idempotency conflict. - `413`: request body exceeds 25 MB. - `422`: validation failed; read `error.errors`. - `429` or `503`: retry according to response headers. ## Routing - Setup/auth first call: `sendmux-getting-started`. - Attachment file paths, presigned upload URLs, and download URLs: `sendmux-attachments`. - Mailbox-centred replies: `sendmux-mailbox-agent`. - CLI-only details: `sendmux-cli`. - Cheapest-call decisions: `sendmux-token-efficient-usage`.