Sending by HTTP

Use the HTTP Sending API for new integrations, batch sending, and retry-safe requests.

Routing follows the send-only key or mailbox key you authenticate with. You cannot choose a provider or delivery group inside an individual send request.

Managed Amazon SES is for transactional email only. Use your own provider for marketing, newsletters, or bulk promotional sends.

Prerequisites

A team with sending access.
A send-only key or mailbox key with email.send.
Enough team balance for the messages you send.
A verified sending-only or sending & receiving custom domain, unless you are testing with the shared domain.

Send one email

curl -X POST https://smtp.sendmux.ai/api/v1/emails/send \
  -H "Authorization: Bearer smx_mbx_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "from": { "email": "hello@example.com", "name": "Your App" },
    "to": { "email": "user@example.com", "name": "Jane Doe" },
    "subject": "Welcome",
    "html_body": "<p>Thanks for signing up.</p>",
    "text_body": "Thanks for signing up."
  }'

A successful request returns 200 OK with a queued message_id.

Send a batch

Send up to 100 messages in one request. The response reports each message by its input index.

curl -X POST https://smtp.sendmux.ai/api/v1/emails/send/batch \
  -H "Authorization: Bearer smx_mbx_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "messages": [
      {
        "from": { "email": "hello@example.com" },
        "to": { "email": "alice@example.com" },
        "subject": "Hello Alice",
        "html_body": "<p>Hi Alice.</p>"
      },
      {
        "from": { "email": "hello@example.com" },
        "to": { "email": "bob@example.com" },
        "subject": "Hello Bob",
        "html_body": "<p>Hi Bob.</p>"
      }
    ]
  }'

A batch can return 200 OK while some messages fail. Check data.summary.failed, then inspect every item in data.results by index. Queued items include a message_id; failed items include error details.

Useful options

Option	Use it for
`cc`, `bcc`	Add more recipients. Each list can contain up to 100 recipients.
`reply_to`	Direct replies to a different address.
`return_path`	Set the envelope sender for bounce handling.
`custom_headers`	Add custom `X-*` headers to the outgoing message.
`attachments`	Attach uploaded `attachment_id` refs, or tiny inline base64 content.
`Idempotency-Key`	Safely retry a request without sending twice.

See the Sending API reference for the full schema.

Error handling

Check the ok field. If it is false, read error.code, error.message, and meta.request_id.

const data = await response.json();

if (!data.ok) {
  console.error(data.error.code, data.error.message, data.meta.request_id);
}

Use Sending API errors for retry and support guidance.

SMTP sending

Use SMTP when an existing tool only supports SMTP delivery.

Attachments

Add files to HTTP send requests.

Idempotency

Make send retries safe with Idempotency-Key.

Sending accounts

Connect providers and control routing before you send.

Getting started

SDKs

CLI

Integrations

AI integrations

Teams and access

Sending

Receiving

Monitoring

Billing

Webhooks

Sending by HTTP

Prerequisites

Send one email

Send a batch

Useful options

Error handling

SMTP sending

Attachments

Idempotency

Sending accounts

​Prerequisites

​Send one email

​Send a batch

​Useful options

​Error handling

​Related guides

SMTP sending

Attachments

Idempotency

Sending accounts

Prerequisites

Send one email

Send a batch

Useful options

Error handling

Related guides