Laravelで文字コードISO-2022-JPのメールを送る

Laravel 5.4で動作確認

<?php

namespace App\Mail;

use Illuminate\Mail\Mailable as BaseMailable;
use Swift;
use Swift_DependencyContainer;
use Swift_Preferences;

class Mailable extends BaseMailable
{
    /**
     * Create a new message instance.
     *
     * @return void
     */
    public function __construct()
    {
        Swift::init(function () {
            Swift_DependencyContainer::getInstance()
               ->register('mime.qpheaderencoder')
               ->asAliasOf('mime.base64headerencoder');
        });

        Swift_Preferences::getInstance()
            ->setCharset('ISO-2022-JP');
    }

    /**
     * {@inheritdoc}
     */
    public function subject($subject)
    {
        $this->subject = sprintf(
            '=?ISO-2022-JP?B?%s?=',
            base64_encode(mb_convert_encoding($subject, 'JIS', 'UTF8'))
        );

        return $this;
    }
}