ZF2 + SMTP + Gmail

composer.json

{
    "require": {
        "zendframework/zend-mail": "^2.5"
    }
}

index.php

<?php

require 'vendor/autoload.php';

use Zend\Mail\Transport\Smtp;
use Zend\Mail\Transport\SmtpOptions;
use Zend\Mail\Message;
use Zend\Mime\Message as MimeMessage;
use Zend\Mime\Part as MimePart;


$message = new Message();
$body = new MimeMessage();
$html = 'Mensagem teste';
$htmlPart = new MimePart($html);
$htmlPart->setType('text/html');

$body->setParts(array($htmlPart));
$message->setEncoding('utf-8')
        ->addTo('emaildestinatario@mail.com')
        ->setFrom('emailremetente@mail.com')
        ->setSubject('Zend Mail')
        ->setBody($body);
$transport = new Smtp();
$transport->setOptions(new SmtpOptions([
    'host' => 'smtp.gmail.com',
    'port' => 587,
    'connection_class' => 'plain',
    'connection_config' => [
        'username' => 'emailremetente@mail.com',
        'password' => 'senha',
        'ssl' => 'tls',
    ]
]));
$transport->send($message);