app.get('/:id/tracker.png', function(request, response, next) {
    var emailId = request.param.id;
    var buf = new Buffer([
        0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00,
        0x80, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x2c,
        0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02,
        0x02, 0x44, 0x01, 0x00, 0x3b
    ]);
    response.set('Content-Type', 'image/png');
    response.end(buf, 'binary');
    db.findOne({ id: emailId }, function(error, email) {
        if(error) return next(error);
        app.emit('event:opened', email);
    });
});

app.on('event:opened', function(email) {
    console.log('Email was opened');
    console.log(email.to);
    console.log(email.subject);
});