<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class RecruitingCampaignRecipient extends Model
{
    use SoftDeletes;
    use Notifiable;

    /**
     * Get the user that owns the phone.
     */
    public function recruitingCampaign()
    {
        return $this->belongsTo('App\RecruitingCampaign');
    }

    /**
     * Get the user that owns the phone.
     */
    public function recruitingVisit()
    {
        return $this->belongsTo('App\RecruitingVisit');
    }

    /**
     * Get the user that is related to the model.
     */
    public function user()
    {
        return $this->belongsTo('App\User');
    }

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

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;

class RecruitingCampaignRecipient extends Model
{
    use SoftDeletes;

    /**
     * Get the user that owns the phone.
     */
    public function recruitingCampaign()
    {
        return $this->belongsTo('App\RecruitingCampaign');
    }

    /**
     * Get the user that owns the phone.
     */
    public function recruitingVisit()
    {
        return $this->belongsTo('App\RecruitingVisit');
    }

    /**
     * Get the user that is related to the model.
     */
    public function user()
    {
        return $this->belongsTo('App\User');
    }
}

--- 
+++ 
@@ -2,12 +2,14 @@
 
 namespace App;
 
+use Illuminate\Notifications\Notifiable;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
 class RecruitingCampaignRecipient extends Model
 {
     use SoftDeletes;
+    use Notifiable;
 
     /**
      * Get the user that owns the phone.
@@ -32,4 +34,14 @@
     {
         return $this->belongsTo('App\User');
     }
+
+    /**
+     * Route notifications for the mail channel.
+     *
+     * @return string
+     */
+    public function routeNotificationForMail()
+    {
+        return $this->email_address;
+    }
 }
Make this a functional notifiable class
