Electronic Mail

Electronic mail ("email" or "e-mail") is an essential part of modern business workflows. Spreadsheets are commonly passed around and processed.

There are NodeJS and other server-side solutions for sending email with attached spreadsheets as well as processing spreadsheets in inboxes.

This demo covers three workflows:

Sending mail covers libraries for sending messages
Reading mail covers libraries for reading messages
Data files covers mailbox file formats

There are a number of caveats when dealing with live mail servers. It is advised to follow connector module documentation carefully and test with new accounts before integrating with important inboxes or accounts.

Live Servers

It is strongly advised to use a test email address before using an important address. One small mistake could erase decades of messages or result in a block or ban from Google services.

App Passwords

Many email providers (including Fastmail, GMail, and Yahoo Mail) require "app passwords" or passwords for "less secure apps". Attempting to connect and send using the account password will throw errors.

Test Account

It is strongly recommended to first test with an independent service provider.

Fastmail

This demo will start with a free 30-day trial of Fastmail. At the time the demo was last tested, no payment details were required.

A valid phone number (for SMS verification) was required.

Create a new Fastmail email account and verify with a mobile number.

Create App Password

Open the settings screen (click on the icon in the top-left corner of the screen and select "Settings").
Select "Privacy & Security" in the left pane, then click "Integrations" near the top of the main page. Click "New app password".
Select any name in the top drop-down (the default "iPhone" can be used). In the second drop-down, select "Mail (IMAP/POP/SMTP)". Click "Generate password".

A new password will be displayed. This is the app password that will be used in the demo script. Copy the displayed password or write it down.

Gmail

This demo will start with a free Gmail account. At the time the demo was last tested, no payment details were required.

A valid phone number (for SMS verification and 2FA) was required.

Create a new Gmail email account and verify with a mobile number.

Create App Password

Click the icon in the top-right corner and click "Manage your Google Account"
Click "Security" in the left column
Enable 2-Step Verification (if it is not currently enabled)
Click "2-Step Verification"
Click the right arrow (>) next to "App passwords".
Type a name ("SheetJS Test") and click "Create".

A new password will be displayed. This is the app password that will be used in the demo script. Copy the displayed password or write it down.

Operations

Sending Mail

Many SheetJS users deploy the nodemailer module in production.

nodemailer supports NodeJS Buffer attachments generated from XLSX.write:

/* write workbook to buffer */
const buf = XLSX.write(workbook, {
  bookType: "xlsb", // <-- write XLSB file
  type: "buffer"    // <-- generate a buffer
});

/* create a message */
const msg = { from: "*", to: "*", subject: "*", text: "*",
  attachments: [
    {
      filename: "SheetJSMailExport.xlsb", // <-- filename
      content: buf                        // <-- data
    }
  ]
}

The file name must have the expected extension for the bookType!

"Supported Output Formats" includes a table showing the file extension required for each supported type.

Send Demo

Tested Deployments

This demo was tested in the following deployments:

Email Provider	Date	Library	Version
`gmail.com`	2024-03-11	`nodemailer`	`6.9.12`
`fastmail.com`	2024-03-11	`nodemailer`	`6.9.12`

Create a new account
Create a new project and install dependencies:

mkdir sheetjs-send
cd sheetjs-send
npm i --save https://cdn.sheetjs.com/xlsx-0.20.2/xlsx-0.20.2.tgz [email protected]

Save the following script to SheetJSend.js:

SheetJSend.js
const XLSX = require('xlsx');
const nodemailer = require('nodemailer');

const transporter = nodemailer.createTransport({
  service: 'fastmail',
  auth: {
    user: '**',
    pass: '**'
  }
});

const wb = XLSX.utils.book_new();
const ws = XLSX.utils.aoa_to_sheet([["Sheet","JS"], ["Node","Mailer"]]);
XLSX.utils.book_append_sheet(wb, ws, "Sheet1");

const buf = XLSX.write(wb, { bookType: "xlsb", type: "buffer" });

const mailOptions = {
  from: "**",
  to: "**",
  subject: "Attachment test",
  text: "if this succeeded, there will be an attachment",
  attachments: [{
    filename: "SheetJSMailExport.xlsb", // <-- filename
    content: buf                        // <-- data
  }]
}

transporter.sendMail(mailOptions, function (err, info) {
  if(err) console.log(err); else console.log(info);
});

Edit SheetJSend.js and replace the highlighted lines:

service: 'fastmail', the value should be one of the supported providers¹
user: "**", the value should be the sender email address
pass: "**" the value should be the app password from earlier
from: "**", the value should be the sender email address
to: "**", the value should be your work or personal email address

Run the script:

node SheetJSend.js

If the process succeeded, the terminal will print a JS object with fields including accepted and response. The recipient inbox should receive an email shortly. The email will include an attachment SheetJSMailExport.xlsb which can be opened in Excel.

The app password must be entered in step 3. If the account password was used, the mailer will fail with a message that includes:

Sorry, you need to create an app password to use this service

Reading Mail

imapflow is a modern IMAP client library.

Parsing attachments is a multi-step dance:

Fetch a message and parse the body structure:

let m = await client.fetchOne(client.mailbox.exists, { bodyStructure: true });
let children = message.bodyStructure.childNodes;

Find all attachments with relevant file extensions:

for(let bs of message.bodyStructure.childNodes) {
  if(bs.disposition?.toLowerCase() != "attachment") continue;
  // look for attachments with certain extensions
  if(!/\.(numbers|xls[xbm]?)$/i.test(bs?.parameters?.name)) continue;
  await process_attachment(bs);
}

Download data and collect into a NodeJS Buffer:

/* helper function to concatenate data from a stream */
const concat_RS = (stream) => new Promise((res, rej) => {
  var buffers = [];
  stream.on("data", function(data) { buffers.push(data); });
  stream.on("end", function() { res(Buffer.concat(buffers)); });
});
async function process_attachment(bs) {
  const { content } = await client.download('*', bs.part);
  /* content is a stream */
  const buf = await concat_RS(content);
  return process_buf(buf, bs.parameters.name);
}

Parse Buffer with XLSX.read:

function process_buf(buf, name) {
  const wb = XLSX.read(buf);
  /* DO SOMETHING WITH wb HERE */
  // print file name and CSV of first sheet
  const wsname = wb.SheetNames[0];
  console.log(name);
  console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wsname]));
}

Receive Demo

Tested Deployments

This demo was tested in the following deployments:

Email Provider	Date	Library	Version
`gmail.com`	2024-03-11	`imapflow`	`1.0.156`
`fastmail.com`	2024-03-11	`imapflow`	`1.0.156`

Create a new account
Create a new project and install dependencies:

mkdir sheetjs-recv
cd sheetjs-recv
npm i --save https://cdn.sheetjs.com/xlsx-0.20.2/xlsx-0.20.2.tgz [email protected]

Save the following script to SheetJSIMAP.js:

SheetJSIMAP.js
const XLSX = require('xlsx');
const { ImapFlow } = require('imapflow');

const client = new ImapFlow({
  host: 'imap.fastmail.com',
  port: 993, secure: true, logger: false,
  auth: {
    user: '**',
    pass: '**'
  }
});

const concat_RS = (stream)  => new Promise((res, rej) => {
  var buffers = [];
  stream.on("data", function(data) { buffers.push(data); });
  stream.on("end", function() { res(Buffer.concat(buffers)); });
});

(async() => {
  await client.connect();
  let lock = await client.getMailboxLock('INBOX'); // INBOX
  try {
    // fetch latest message source with body structure
    let message = await client.fetchOne(client.mailbox.exists, { bodyStructure: true });
    for(let bs of message.bodyStructure.childNodes) {
      if(bs.disposition?.toLowerCase() != "attachment") continue;
      // look for attachments with certain extensions
      if(!/\.(numbers|xls[xbm]?)$/i.test(bs?.parameters?.name)) continue;

      // download data
      const { content } = await client.download('*', bs.part);
      const buf = await concat_RS(content);

      // parse
      const wb = XLSX.read(buf);

      // print file name and CSV of first sheet
      const wsname = wb.SheetNames[0];
      console.log(bs.parameters.name);
      console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wsname]));
    }
  } finally { lock.release(); }
  await client.logout();
})();

Edit SheetJSIMAP.js and replace the highlighted lines:

user: "**", the value should be the account address
pass: "**" the value should be the app password from earlier
host: 'imap.fastmail.com', the value should be the host name:

Service	`host` value
`gmail.com`	`imap.gmail.com`
`fastmail.com`	`imap.fastmail.com`

Download https://docs.sheetjs.com/pres.numbers . Using a different account, send an email to the test account and attach the file. At the end of this step, the test account should have an email in the inbox that has an attachment.
Run the script:

node SheetJSIMAP.js

The output should include the file name (pres.numbers) and the CSV:

pres.numbers
Name,Index
Bill Clinton,42
GeorgeW Bush,43
Barack Obama,44
Donald Trump,45
Joseph Biden,46

Data Files

Electronic discovery commonly involves email spelunking. There are a number of proprietary mail and email account file formats.

PST

The exposition has been moved to a separate page.

The list of services can be found in lib/well-known/services.json in the NodeMailer project. ↩

Live Servers​

App Passwords​

Test Account​

Fastmail​

Gmail​

Operations​

Sending Mail​

Send Demo​

Reading Mail​

Receive Demo​

Data Files​

PST​

Footnotes​