# Send emails with Next.js

> Send email from a Next.js Route Handler or Server Action using the mailblastr SDK — your API key stays on the server.

In Next.js you should call MailBlastr from **server-only code** — a Route Handler (`app/api/.../route.ts`) or a Server Action — never from a Client Component. That keeps your `mb_` API key out of the browser bundle.

Install the SDK (`npm install mailblastr`) and import it in your server files. This guide adds a `POST /api/send` Route Handler and shows the equivalent Server Action.

## Prerequisites

1. A **verified domain** for your `from` address. ([guide](https://www.mailblastr.com/docs/domains/managing))
2. An **API key** stored as an environment variable (e.g. `MAILBLASTR_API_KEY` in `.env.local`). ([Authentication](https://www.mailblastr.com/docs/authentication))
3. A **Next.js 13.4+ App Router** project (Route Handlers / Server Actions) and `npm install mailblastr`.

## Route Handler

Create `app/api/send/route.ts`. Because the file runs only on the server, `process.env.MAILBLASTR_API_KEY` is never exposed to the client.

**app/api/send/route.ts**

```ts
import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr(process.env.MAILBLASTR_API_KEY);

export async function POST() {
  const { data, error } = await mb.emails.send({
    from: 'Acme <hello@yourdomain.com>',
    to: ['delivered@example.com'],
    subject: 'Hello from Next.js',
    html: '<p>Sent from a Route Handler.</p>',
  });

  if (error) {
    return Response.json({ error: error.message }, { status: 400 });
  }

  return Response.json(data);
}
```

## Or a Server Action

If you are submitting a form, a Server Action keeps the key server-side too. The `'use server'` directive guarantees the function never ships to the client.

**app/actions.ts**

```ts
'use server';

import { MailBlastr } from 'mailblastr';

const mb = new MailBlastr(process.env.MAILBLASTR_API_KEY);

export async function sendEmail(formData: FormData) {
  const { data, error } = await mb.emails.send({
    from: 'Acme <hello@yourdomain.com>',
    to: [String(formData.get('email'))],
    subject: 'Thanks for signing up',
    html: '<p>Welcome aboard!</p>',
  });

  if (error) {
    throw new Error(error.message);
  }

  return data.id;
}
```

## Handling the response

Every SDK call returns `{ data, error }`. On success `data.id` is the created email's ID; on failure `error` is set and `data` is `null`. The examples above relay a clean error to the client without leaking the key. Use the `id` to [retrieve the email](https://www.mailblastr.com/docs/api/emails-get) or correlate [webhook](https://www.mailblastr.com/docs/webhooks/overview) events.

> **Warning:** Only reference `MAILBLASTR_API_KEY` in server files (Route Handlers, Server Actions, `getServerSideProps`). Never prefix it with `NEXT_PUBLIC_` and never read it in a Client Component — that would inline the secret into the browser bundle.

## Next steps

- See the full [Send Email API](https://www.mailblastr.com/docs/api/emails-send) reference.
- Review [Authentication](https://www.mailblastr.com/docs/authentication) for key permissions (a `sending_access` key is ideal here).
- New to the API? Start with the [Quickstart](https://www.mailblastr.com/docs/quickstart).