Worked on the server

front/form.js

 var xhrSend = new XMLHttpRequest();
 xhrSend.onreadystatechange = function() {
     if (xhrSend.readyState == XMLHttpRequest.DONE) {
-        console.log(xhrSend);
+        console.log(xhrSend.response);
     }
 };
 

package.json

     "express": "4.14.0",
     "node-minify": "1.3.9",
     "nodemailer": "2.4.2",
-    "printit": "0.1.20"
+    "printit": "0.1.20",
+    "pug": "2.0.0-beta6"
   },
   "license": {
     "type": "GPL-3.0",

server.js

+"use strict"
+var pug         = require('pug');
+var nodemailer  = require('nodemailer');
+var settings    = require('./settings');
+
+// Web server
 var bodyParser  = require('body-parser');
 var express     = require('express');
 var app = express();
     date: true
 });
 
+var transporter = nodemailer.createTransport(settings.mailserver);
 
 // Serve static (JS + HTML) files
 app.use(express.static('front'));
+// Body parsing
 app.use(bodyParser.urlencoded({ extended: true }));
 app.use(bodyParser.json());
 
-
+// A request on /send with user input = mail to be sent
 app.post('/send', function(req, res, next) {
-    res.header('Access-Control-Allow-Origin', '*');
-    res.status(200).send();
-    console.log(req.body);
+    // params will be used as:
+    // - values for html generation from the pug template
+    // - parameters for sending the mail(s)
+    let params = {
+        subject: req.body.subj,
+        from: req.body.name + ' <' + req.body.addr + '>',
+        html: req.body.text
+    };
+    
+    // Replacing the mail's content with HTML from the pug template
+    // Commenting the line below will bypass the generation and only user the
+    // text entered by the user
+    params.html = pug.renderFile('template.pug', params);
+    
+    log.info('Sending message from ' + content.from);
+    
+    // Send the email to all users
+    sendMails(params, function(err, infos) {
+        if(err) {
+            log.error(err)
+        }
+        logStatus(infos);
+    }, function() {
+        res.header('Access-Control-Allow-Origin', '*');
+        res.status(200).send();
+    })
 });
 
 
-app.listen(1970, function() {
-    log.info("Server started");
+// Use either the default port or the one chosen by the user (PORT env variable)
+var port = process.env.PORT || 1970;
+// Start the server
+app.listen(port, function() {
+    log.info("Server started on port " + port);
 });
+
+
+// Send mails to the recipients specified in the JSON settings file
+// content: object containing mail params
+//  {
+//      subject: String
+//      from: String (following RFC 1036 (https://tools.ietf.org/html/rfc1036#section-2.1.1))
+//      html: String
+//  }
+// update(next, infos): Called each time a mail is sent with the infos provided
+//                      by nodemailer
+// done(): Called once each mail has been sent
+function sendMails(params, update, done) {
+    let mails = settings.recipients.map((recipient) => {
+        return new Promise((sent) => {            
+            params.to = recipient;
+            
+            transporter.sendMail(params, (err, infos) => {
+                sent();
+                if(err) {
+                    return next(err, recipient);
+                }
+                next(null, infos);
+            });
+        });
+    });
+    Promise.all(mails).then(done);
+}
+
+
+// Produces log from the infos provided by nodemailer
+// infos: infos provided by nodemailer
+// return: nothing
+function logStatus(infos) {
+    if(infos.accepted.length) {
+        log.info('Message sent to ' + status.accepted[0]);
+    }
+    if(infos.rejected.length) {
+        log.info('Message failed to send to ' + status.rejected[0]);
+    }
+}

settings.example.json

+{
+    "mailserver": {
+        "pool": true,
+        "host": "mail.example.tld",
+        "port": 465,
+        "secure": true,
+        "auth": {
+            "user": "noreply@noreply.tld",
+            "pass": "hackme"
+        }
+    },
+    "recipients": [
+        "you@example.tld",
+        "someone.else@example.com"
+    ]
+}

template.pug

             span(style="font-weight:bold") Sent from: 
             span= from
         
-        p= text
+        p= html