Q:

Use Laravel routeNotifcationForMail() to send to multiple emails addresses?

I'm using the Notifiable trait on my Model.
User has comma-separated list of subscribed emails (string).
The documentation and my background reading suggests that this will only route to a single email address.
<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    /**
     * Route notifications for the mail channel.
     *
     * @return string
     */
    public function routeNotificationForMail()
    {
        return $this->email_address;
    }
}

Laravel 5.3 Notifications
I've also read Matt Stauffer on Notifications but can't see an answer there.
My NotificationClass->toMail() is as follows.
/**
 * Get the mail representation of the notification.
 *
 * @param Store $store
 * @return mixed
 * @throws Exception
 */
public function toMail(User $user)
{
    return (new MailMessage)->view('notifications.emails.activity-roundup', compact('user'));
}

A:

I guess you want code below since you can send array (see here):
/**
 * Route notifications for the mail channel.
 *
 * @return string
 */
public function routeNotificationForMail()
{
    return $this->emailsToArray();
}

private function emailsToArray() {
    if (is_null($this->email_addresses)) {
        return $this->email; //default email
    }
    //perform more checks that you need
    return array_map('trim', explode(',', $this->email_addresses))
}

