nodemailer-smtp-pool.js

'use strict';
// npm install nodemailer nodemailer-smtp-pool
var nodemailer = require('nodemailer');
var smtpPool = require('nodemailer-smtp-pool');

// Create a SMTP transporter object
var transport = nodemailer.createTransport(smtpPool({
    host: 'smtp.gmail.com',
    port: 465,
    secure: true,
    auth: {
        user: 'username',
        pass: 'password'
    },
    // use up to 5 parallel connections, default is 5
    maxConnections: 5,
    // do not send more than 10 messages per connection, default is 100
    maxMessages: 10,
    // no not send more than 5 messages in a second, default is no limit
    rateLimit: 5
}));

console.log('SMTP Configured');

// Message object
var message = {

    // sender info
    from: 'Sender Name <[email protected]>',

    // Comma separated list of recipients
    to: '"Receiver Name" <[email protected]>',

    // Subject of the message
    subject: 'Nodemailer is unicode friendly ✔', //

    headers: {
        'X-Laziness-level': 1000
    },

    // plaintext body
    text: 'Hello to myself!',

    // HTML body
    html: '<p><b>Hello</b> to myself <img src="cid:[email protected]"/></p>' +
        '<p>Here\'s a nyan cat for you as an embedded attachment:<br/><img src="cid:[email protected]"/></p>',

    // Apple Watch specific HTML body
    watchHtml: '<b>Hello</b> to myself',

    // An array of attachments
    attachments: [

        // String attachment
        {
            filename: 'notes.txt',
            content: 'Some notes about this e-mail',
            contentType: 'text/plain' // optional, would be detected from the filename
        },

        // Binary Buffer attachment
        {
            filename: 'image.png',
            content: new Buffer('iVBORw0KGgoAAAANSUhEUgAAABAAAAAQAQMAAAAlPW0iAAAABlBMVEUAAAD/' +
                '//+l2Z/dAAAAM0lEQVR4nGP4/5/h/1+G/58ZDrAz3D/McH8yw83NDDeNGe4U' +
                'g9C9zwz3gVLMDA/A6P9/AFGGFyjOXZtQAAAAAElFTkSuQmCC', 'base64'),

            cid: '[email protected]' // should be as unique as possible
        },

        // File Stream attachment
        {
            filename: 'nyan cat ✔.gif',
            path: __dirname + '/assets/nyan.gif',
            cid: '[email protected]' // should be as unique as possible
        }
    ]
};

console.log('Sending Mail');
transporter.sendMail(message, function(error, info) {
    if (error) {
        console.log('Error occurred');
        console.log(error.message);
        return;
    }
    console.log('Message sent successfully!');
    console.log('Server responded with "%s"', info.response);
});

So if I use sendMail few times in a loop do they all get pooled?

for(let i=0; i<5; i++) {
    let changedMessageObj = {}; // add some customizations to message obj like change to field
    transporter.sendMail(message, handler);
}

@anshulguleria, any luck figuring this out? I am facing a similar situation and need help in this