PHP - 将包模型扩展到您自己的模型

I am currently trying to setup a simple web-app, using Laravel Mailbox. I can see that I can define a custom model to use in the config file:

    /*
     * The model class to use when converting an incoming email to a message.
     * It must extend the default model class
     */
    'model' => \BeyondCode\Mailbox\InboundEmail::class,

Above is the default model it uses.

I have changed it to:

    /*
     * The model class to use when converting an incoming email to a message.
     * It must extend the default model class
     */
    'model' => Email::class,

Now, I wish to use my own model, because I want to store the e-mails on another table. For this, I have created my own model, and trying to extend the original one from the package, but overwrite the $table for example.

App/Email.php:

namespace App;

use BeyondCode\Mailbox\InboundEmail as InboundEmail;

class Email extends InboundEmail
{
    protected static function boot()
    {
        parent::boot();
    }

    protected $table = 'emails';
}

However, above gives me below error:

Undefined property: App\Email::$message {"exception":"[object] (ErrorException(code: 0): Undefined property: App\\Email::$message at /Users/Username/Sites/playground/vendor/beyondcode/laravel-mailbox/src/InboundEmail.php:130)

I suspect it is because I don't have the original methods in my own model App/Email.php, that are present in the package model.

Isn't there a way that I can use my own model, by extending the package model, but without copying the content of the package model into my own?