Sending email

Mailing can be used just for developing HTML emails, but we think it works best when it’s also used to send. This way you can render emails dynamically based on props at runtime and keep all of your templating logic in one place.

The main API for using Mailing from your app is sendMail(). This function is built with nodemailer, so you can pass in any options that nodemailer supports. When you pass in a React component instead of an HTML string, the component is rendered to HTML and sent as the email body.

If you’re triggering sends from a non-node app, you can also access sendMail via the REST API.

Before sending email, you'll need to configure a transport. This is the SMTP service that will send your email.

Mailing is transport agnostic, here are a few we like:

  • Sendgrid: cheap and reliable, pairs well with other Twilio products
  • SES: cheap and reliable, pairs well with AWS
  • Postmark: more expensive but great developer experience

Once you've selected one of these, set your SMTP credentials they give you in emails/index.ts.

Here's a working example using Postmark:

const sendMail = buildSendMail({
  transport: nodemailer.createTransport({
    host: "",
    port: 587,
    auth: {
      user: process.env.POSTMARK_API_KEY,
      pass: process.env.POSTMARK_API_KEY,
  defaultFrom: "Steven from Dub <>",
  configPath: "./mailing.config.json",
  // optional
  processHtml: (html: string) =>
    htmlMinify(html, {
      caseSensitive: true,
      collapseWhitespace: true,
      minifyCSS: true,
      removeComments: true,
      removeEmptyAttributes: true,

You'll notice that environment variables are used to store credentials. This is a good practice for security, but you can also hardcode them for testing.

Once you’ve configured sendMail in emails/index.ts, you can import and call it. It’s an async function so if you need to wait for the send to complete, you can use await:

import sendMail from “path/to/emails”;

await sendMail({
  to: "",
  subject: "Hello",
  component: <MyTemplate data={myData} />

Note that sendMail must be called from your back-end (e.g. an API route in your NextJS app) because it uses secrets. We recommend configuring it with environment variables.

sendMail (mail: ComponentMail) => Promise<T | undefined>

Sends an email using the configured transport. It extends the sendMail function from nodemailer and can accomodate any options that nodemailer supports.

Common ComponentMail options

  • component – The React component to render as the email body. If you pass in a string for html, this will be ignored
  • dangerouslyForceDeliver – If true, the email will be sent even if the NODE_ENV is not production. Use with caution.
  • forcePreview – If true, the email will be intercepted by the preview server
  • previewServerUrl – If you have changed the port of the mailing preview server, you can set it here (default: http://localhost:3883)
  • listName – The name of the list to send the email to. Read more about lists
  • from – The email address of the sender. If not provided, the defaultFrom address configured in buildSendMail will be used.
  • to – Comma separated list or an array of recipients email addresses that will appear on the To: field
  • cc – Comma separated list or an array of recipients email addresses that will appear on the Cc: field
  • bcc – Comma separated list or an array of recipients email addresses that will appear on the Bcc: field
  • subject – The subject of the email
  • text – The plaintext version of the message as an Unicode string, Buffer, Stream
  • html – The HTML version of the message as an Unicode string, Buffer, Stream
  • attachments – An array of attachment objects (see nodemailer docs for details). Attachments can be used for embedding images as well.

Q: How can I send from my Django/Rails/PHP app?

A: Once you've configured your transport, you can use the REST API to send emails from any app. To use it you'll need to deploy and set up an API key.

Q: Can I have multiple transports?

A: Yes, you can build multiple sendMail functions and import them as needed. This is useful if you want to send emails from different accounts or with different settings. For example Postmark encourages users to have one transport for transactional emails and another for marketing emails. Just make sure to export one of them as the default to be used by the development preview server and the REST API.