index.js

import express from "express";
import net from "net";
import dns from "dns";
const app = express();
import cors from "cors";
import bodyParser from "body-parser";
const PORT = process.env.PORT || 3333;


app.use(cors());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());


app.get("/", (_, res) => {
  return res
    .status(200)
    .json({ success: true, message: "Welcome on Mailtester API" });
});

const validateEmail = (email) => {
  const validSyntax = /^[\w-\.]+@([\w-]+\.)+[\w-]{2,}$/.test(email);
  if (!validSyntax) {
    return Promise.resolve(false);
  }

  const domain = email.split("@")[1];
  const ports = [25, 587, 465];

  return new Promise((resolve) => {
    const tryNextPort = (index) => {
      if (index >= ports.length) {
        resolve(false);
        return;
      }

      const port = ports[index];

      dns.resolveMx(domain, (err, mxRecords) => {
        if (err || !mxRecords || mxRecords.length === 0) {
          tryNextPort(index + 1);
        } else {
          const smtp = net.createConnection(port, mxRecords[0].exchange);
          let connected = false;
          const timeout = 3000; // 3 seconds
          const timeoutId = setTimeout(() => {
            if (!connected) {
              smtp.destroy();
              tryNextPort(index + 1);
            }
          }, timeout);
          smtp.on("connect", () => {
            connected = true;
            clearTimeout(timeoutId);
            smtp.destroy();
            resolve(true);
          });
          smtp.on("error", () => {
            tryNextPort(index + 1);
          });
        }
      });
    };

    tryNextPort(0);
  });
};

app.get("/single-mail/:email", async (req, res) => {
  const email = req.params.email;

  validateEmail(email)
    .then((response) => {
      if (response) {
        return res.status(200).json({
          success: true,
          message: `${email} is a valid email address.`,
        });
      } else {
        return res.status(406).json({
          success: false,
          message: `${email} is NOT a valid email address.`,
        });
      }
    })
    .catch((err) => {
      return res.status(406).json({
        success: false,
        message: `${email} is NOT a valid email address.`,
        error: err,
      });
    });
});

app.post("/bulk-mails", (req, res) => {
  if (!req.body) {
    return res.status(400).json({
      success: false,
      message: "Body must be provided",
    });
  }

  if (!req.body.emails) {
    return res.status(400).json({
      success: false,
      message: "Emails must be provided",
    });
  }
  const emails = req.body.emails;

  if (!Array.isArray(emails)) {
    return res.status(400).json({
      success: false,
      message: "Emails must be an array",
    });
  }

  const validEmails = [];
  const invalidEmails = [];

  for (let email of emails) {
    validateEmail(email)
      .then((response) => {

        if (response) {
          validEmails.push(email);
        } else {
          invalidEmails.push(email);
        }
        
        if(emails.length === validEmails.length + invalidEmails.length) {
          return res.status(200).json({
            success: true,
            message: "Emails validated",
            validEmails: validEmails,
            invalidEmails: invalidEmails,
          });
        }
      })
      .catch(_ => {
        invalidEmails.push(email);
      });
  } 
});

app.listen(PORT, () => {
  console.info(`App listening at http://localhost:${PORT}`);
});