validate.js

#!/usr/bin/env node

/**
 * Very simple node script to validate an email address against its SMTP server.
 *
 * Usage:
 *   node validate.js email@mail.com
 *
 * This script uses the following process to validate an email address:
 *   1. Get the domain of the email
 *   2. Grab the DNS MX records for that domain
 *   3. Create a TCP connection to the smtp server
 *   4. Send a EHLO message
 *   5. Send a MAIL FROM message
 *   6. Send a RCPT TO message
 *   7. Return an object indicating whether the email passed SMTP validation:
 *        {
 *          valid: true,          // true: email is valid, false: email is
 *                                // invalid.
 *          err: "error message", // If an error is encountered then this will
 *                                // contain the error string. If there is no
 *                                // error then this value is null.
 *        }
 *
 * @author Mike Ratcliffe
 */

const dns = require("dns");
const net = require("net");

if (process.argv.length < 3) {
  console.log(
    "Very simple node script to validate an email address against its SMTP server.\n\nUsage:\n  node validate.js email@mail.com"
  );
  return;
}

const dnsPromises = dns.promises;
const email = process.argv.pop();

(async () => {
  const start = new Date();

  await validate(email, 3000, (valid, err) => {
    console.log(`valid`, valid);
    console.log(`err`, err);

    console.log(`Run time: ${new Date() - start}ms`);
  });
})();

/**
 *
 * @param {String} email
 *        email to validate.
 * @param {Number} timeout
 *        timeout in ms.
 * @param {Function} callback
 *        Callback function e.g. myFunc(valid, err) {}
 */
async function validate(email, timeout, callback) {
  const domain = email.split("@")[1];
  const [{ exchange }] = await dnsPromises.resolveMx(domain);

  let receivedData = false;
  let timedOut = false;

  const socket = net.createConnection(25, exchange);
  socket.setEncoding("ascii");
  socket.setTimeout(timeout);
  socket.on("error", (error) => {
    console.log("error", error);
    socket.emit("fail", error);
  });
  socket.on("close", (hadError) => {
    if (!receivedData && !hadError && !timedOut) {
      callback(
        false,
        "Mail server closed connection without sending any data."
      );
    }
  });
  socket.on("fail", (msg) => {
    if (socket.writable && !socket.destroyed) {
      socket.write(`quit\r\n`);
      socket.end();
      socket.destroy();
    }
    callback(false, msg);
  });

  socket.on("success", () => {
    if (socket.writable && !socket.destroyed) {
      socket.write(`quit\r\n`);
      socket.end();
      socket.destroy();
    }
    callback(true, null);
  });

  const commands = [
    `helo ${exchange}\r\n`,
    `mail from: <${email}>\r\n`,
    `rcpt to: <${email}>\r\n`,
  ];
  let i = 0;
  socket.on("next", () => {
    if (i < 3) {
      if (socket.writable) {
        socket.write(commands[i++]);
      } else {
        socket.emit("fail", "SMTP communication unexpectedly closed.");
      }
    } else {
      socket.emit("success");
    }
  });

  socket.on("timeout", () => {
    timedOut = true;
    socket.emit("fail", "Timeout");
  });

  socket.on("connect", () => {
    socket.on("data", (msg) => {
      receivedData = true;

      if (hasCode(msg, 220) || hasCode(msg, 250)) {
        socket.emit("next", msg);
      } else if (hasCode(msg, 550)) {
        socket.emit("fail", "Mailbox not found.");
      } else {
        // Possible error codes
        const ErrorCodes = {
          211: "SMTP Error: A system status or help reply.",
          214: "SMTP Error: Help Message.",
          220: "SMTP Error: The server is ready.",
          221: "SMTP Error: The server is ending the conversation.",
          250: "SMTP Error: The requested action was completed.",
          251: "SMTP Error: The specified user is not local, but the server will forward the mail message.",
          354: 'SMTP Error: This is a reply to the DATA command. After getting this, start sending the body of the mail message, ending with "\r\n.\r\n."',
          421: "SMTP Error: The mail server will be shut down. Save the mail message and try again later.",
          450: "SMTP Error: The mailbox that you are trying to reach is busy. Wait a little while and try again.",
          451: "SMTP Error: The requested action was not done. Some error occurmiles in the mail server.",
          452: "SMTP Error: The requested action was not done. The mail server ran out of system storage.",
          500: "SMTP Error: The last command contained a syntax error or the command line was too long.",
          501: "SMTP Error: The parameters or arguments in the last command contained a syntax error.",
          502: "SMTP Error: The mail server has not implemented the last command.",
          503: "SMTP Error: The last command was sent out of sequence. For example, you might have sent DATA before sending RECV.",
          504: "SMTP Error: One of the parameters of the last command has not been implemented by the server.",
          550: "SMTP Error: The mailbox that you are trying to reach can't be found or you don't have access rights.",
          551: "SMTP Error: The specified user is not local; part of the text of the message will contain a forwarding address.",
          552: "SMTP Error: The mailbox that you are trying to reach has run out of space. Store the message and try again tomorrow or in a few days-after the user gets a chance to delete some messages.",
          553: "SMTP Error: The mail address that you specified was not syntactically correct.",
          554: "SMTP Error: The mail transaction has failed for an unknown reason.",
        };

        const [code] = Object.keys(ErrorCodes).filter((x) => hasCode(msg, x));
        socket.emit("fail", ErrorCodes[code] || "Unrecognized SMTP response.");
      }
    });
  });

  function hasCode(message, code) {
    return (
      message.indexOf(`${code}`) === 0 || message.indexOf(`${code}\n`) > -1
    );
  }
}