Using PHPMailer

app.php

<?php

require __DIR__ . '/vendor/autoload.php';

use PHPWorldWide\Mailer;
$test = new Mailer();

composer.json

{
    "require": {
        "phpmailer/phpmailer": "^5.2"
    },
    "autoload": {
        "psr-4": {"PHPWorldWide\\": "src/"}
    }
}

Mailer.php

<?php

// this file is inside src folder

namespace PHPWorldWide;

use PHPMailer;

class Mailer
{
      public function __construct()
      {
        $mailer = new PHPMailer();
        var_dump($mailer->Version);
      }
}