postal-mime

postal-mime is an email parsing library that runs in browser environments (including Web Workers) and serverless functions (like Cloudflare Email Workers). It takes in a raw email message (RFC822 format) and outputs a structured object containing headers, recipients, attachments, and more.

Tip
PostalMime is developed by the makers of EmailEngine—a self-hosted email gateway that provides a REST API for IMAP and SMTP servers and sends webhooks whenever something changes in registered accounts.

Table of Contents

• Source
• Demo
• Installation
• Usage
  • Browser
  • Node.js
  • Cloudflare Email Workers
• API
  • PostalMime.parse()
  • Utility Functions
    • addressParser()
    • decodeWords()
• License

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Source

The source code is available on GitHub.

Demo

Try out a live demo using the example page.

Installation

Install the module from npm:

npm install postal-mime

Usage

You can import the PostalMime class differently depending on your environment:

Browser

To use PostalMime in the browser (including Web Workers), import it from the src folder:

import PostalMime from './node_modules/postal-mime/src/postal-mime.js';

const email = await PostalMime.parse(`Subject: My awesome email 🤓
Content-Type: text/html; charset=utf-8

<p>Hello world 😵‍💫</p>`);

console.log(email.subject); // "My awesome email 🤓"

Node.js

In Node.js (including serverless functions), import it directly from postal-mime:

import PostalMime from 'postal-mime';
import util from 'node:util';

const email = await PostalMime.parse(`Subject: My awesome email 🤓
Content-Type: text/html; charset=utf-8

<p>Hello world 😵‍💫</p>`);

// Use 'util.inspect' for pretty-printing
console.log(util.inspect(email, false, 22, true));

Cloudflare Email Workers

Use the message.raw as the raw email data for parsing:

import PostalMime from 'postal-mime';

export default {
    async email(message, env, ctx) {
        const email = await PostalMime.parse(message.raw);

        console.log('Subject:', email.subject);
        console.log('HTML:', email.html);
        console.log('Text:', email.text);
    }
};

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API

PostalMime.parse()

PostalMime.parse(email, options) -> Promise<ParsedEmail>

• email: An RFC822 formatted email. This can be a string, ArrayBuffer/Uint8Array, Blob (browser only), Buffer (Node.js), or a ReadableStream.
• options: Optional configuration object:
  • rfc822Attachments (boolean, default: false): Treat message/rfc822 attachments without a Content-Disposition as attachments.
  • forceRfc822Attachments (boolean, default: false): Treat all message/rfc822 parts as attachments.
  • attachmentEncoding (string, default: "arraybuffer"): Determines how attachment content is decoded in the parsed email:
    • "base64"
    • "utf8"
    • "arraybuffer" (no decoding, returns ArrayBuffer)
  • maxNestingDepth (number, default: 256): Maximum allowed MIME part nesting depth. Throws an error if exceeded.
  • maxHeadersSize (number, default: 2097152): Maximum allowed total header size in bytes (default 2MB). Throws an error if exceeded.

Returns: A Promise that resolves to a structured object with the following properties:

• headers: An array of header objects, each containing:
  • key: Lowercase header name (e.g., "dkim-signature").
  • value: Unprocessed header value as a string.
• from, sender: Processed address objects:
  • name: Decoded display name, or an empty string if not set.
  • address: Email address.
• deliveredTo, returnPath: Single email addresses as strings.
• to, cc, bcc, replyTo: Arrays of processed address objects (same structure as from).
• subject: Subject line of the email.
• messageId, inReplyTo, references: Values from their corresponding headers.
• date: The email’s sending time in ISO 8601 format (or the original string if parsing fails).
• html: String containing the HTML content of the email.
• text: String containing the plain text content of the email.
• attachments: Array of attachment objects:
  • filename
  • mimeType
  • disposition (e.g., "attachment", "inline", or null)
  • related (boolean, true if it’s an inline image)
  • contentId
  • content (array buffer or string, depending on attachmentEncoding)
  • encoding (e.g., "base64")

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Utility Functions

addressParser()

import { addressParser } from 'postal-mime';

addressParser(addressStr, opts) -> Array

• addressStr: A raw address header string.
• opts: Optional configuration:
  • flatten (boolean, default: false): If true, ignores address groups and returns a flat array of addresses.

Returns: An array of address objects, which can be nested if address groups are present.

Example:

const addressStr = '=?utf-8?B?44Ko44Od44K544Kr44O844OJ?= <support@example.com>';
console.log(addressParser(addressStr));
// [ { name: 'エポスカード', address: 'support@example.com' } ]

decodeWords()

import { decodeWords } from 'postal-mime';

decodeWords(encodedStr) -> string

• encodedStr: A string that may contain MIME encoded-words.

Returns: A Unicode string with all encoded-words decoded.

Example:

const encodedStr = 'Hello, =?utf-8?B?44Ko44Od44K544Kr44O844OJ?=';
console.log(decodeWords(encodedStr));
// Hello, エポスカード

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License

© 2021–2025 Andris Reinman

postal-mime is licensed under the MIT No Attribution license.