Alternatives

In addition to plain‑text and HTML bodies, you can embed alternative representations of the same content—for example, Markdown or a calendar invite. The email client chooses the representation that best fits the recipient’s environment. Alternatives are most often used for calendar events and other machine‑readable formats.

Prefer icalEvent for calendar invites

If you want to send a calendar event, consider the icalEvent option instead. See Calendar events for details.

How alternatives differ from attachments

Alternative objects accept exactly the same fields as attachment objects. The only difference is where Nodemailer places them in the MIME tree:

Purpose	MIME container
Attachments	multipart/mixed or multipart/related
Alternatives	multipart/alternative

Usage

const message = {
  // ...
  html: "<b>Hello world!</b>",
  alternatives: [
    {
      contentType: "text/x-web-markdown",
      content: "**Hello world!**",
    },
  ],
};

You can include as many alternative bodies as you need. Place the most preferred version last—the majority of clients read the list from top to bottom and render the last format they understand.