Transactional email API for the AI era.

Node.js / TypeScript

import { Nitrosend } from '@nitrosend/sdk';

const ns = new Nitrosend({ apiKey: process.env.NITROSEND_API_KEY });

await ns.messages.send({
  from: '[email protected]',
  to: '[email protected]',
  subject: 'Welcome to Acme',
  html: '<p>Your account is ready.</p>',
});

cURL

curl -X POST https://api.nitrosend.com/v1/my/messages \
  -H "Authorization: Bearer $NITROSEND_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "[email protected]",
    "to": "[email protected]",
    "subject": "Welcome to Acme",
    "html": "<p>Your account is ready.</p>"
  }'

Python

import os, requests

requests.post(
    "https://api.nitrosend.com/v1/my/messages",
    headers={"Authorization": f"Bearer {os.environ['NITROSEND_API_KEY']}"},
    json={
        "from": "[email protected]",
        "to": "[email protected]",
        "subject": "Welcome to Acme",
        "html": "<p>Your account is ready.</p>",
    },
)

From Claude Code (REST/SDK)

# One-time install
claude mcp add --transport http nitrosend https://api.nitrosend.com/mcp

# Then, in Claude Code:
"Add the Nitrosend SDK call for sending a welcome email from
 [email protected] when a user signs up. Keep it idempotent."

What is a transactional email API?

A transactional email API lets developers send one-to-one emails triggered by application events: signup confirmations, password resets, receipts, magic links, invoices. Unlike marketing email (sent to lists), transactional email is sent to a single recipient in response to an action. A good transactional API gives you high deliverability, low latency, webhooks for delivery events, template rendering, and clean logs.

What is the best transactional email API in 2026?

The right API depends on your stack. Resend and Postmark are strong developer-first choices. Amazon SES is the cheapest at scale but requires you to build the platform layer yourself. Nitrosend combines transactional, marketing, and automation in one account, built AI-agent-first with REST/SDK for transactional sends and a full-product MCP workflow server for campaigns and flows.

Does Nitrosend support MCP for AI agents?

Yes. Nitrosend ships a first-party MCP server at https://api.nitrosend.com/mcp for campaigns, flows, templates, tests, and approvals. Transactional app sends use the REST API or SDK, so agents should wire those calls into your application code rather than calling a one-off MCP send tool.

Can I bring my own sending infrastructure?

Yes. On Pro, Ultra, and Enterprise you can BYO SendGrid, Amazon SES, Mailgun, Postmark, or Resend credentials. Nitrosend handles the platform (templates, flows, logs, AI, MCP) and your existing provider handles the actual SMTP. No double-pay, no domain reputation reset.

How much does transactional email cost?

Nitrosend Free gives you 8,000 emails to start, then 500/month at $0. Pro is $20/month for 20,000 emails. Ultra is $100/month for 125,000 emails. Enterprise starts at 500K+. All plans include unlimited contacts, BYO keys on paid tiers, and full MCP/API/CLI access. Overages are $0.19/100 on Pro and $0.15/100 on Ultra.

Does Nitrosend have a Node.js SDK?

Yes. @nitrosend/sdk is on npm. Install with npm i @nitrosend/sdk, then const ns = new Nitrosend({ apiKey }) and call ns.messages.send({ from, to, subject, html }). Python and Ruby SDKs ship next. For non-Node environments use the REST API directly at https://api.nitrosend.com.

What's the difference between transactional email and marketing email?

Transactional email is triggered by an action and sent to one person (password reset, order receipt, magic link). Marketing email is sent to a list with consent-based targeting (newsletters, product announcements, drip campaigns). They typically run on separate sending infrastructure because their deliverability profiles differ. Nitrosend unifies both so you don't need two tools.

What webhook events does the API support?

Sent, delivered, opened, clicked, bounced, complained, unsubscribed, and failed. Webhooks are signed with HMAC-SHA256 and retried with exponential backoff. Payloads include the original message ID, recipient, timestamp, and event-specific metadata.