Add support for setting mail notification priority.

src/Illuminate/Notifications/Channels/MailChannel.php

@@ -70,6 +70,10 @@ public function send($notifiable, Notification $notification)
             foreach ($message->rawAttachments as $attachment) {
                 $m->attachData($attachment['data'], $attachment['name'], $attachment['options']);
             }
+
+            if($message->priority !== null) {
+                $m->setPriority($message->priority);
+            }
         });
     }
 }

src/Illuminate/Notifications/Messages/MailMessage.php

@@ -49,6 +49,13 @@ class MailMessage extends SimpleMessage
      */
     public $rawAttachments = [];
 
+    /**
+     * Priority level of the message.
+     *
+     * @var int
+     */
+    public $priority = null;
+
     /**
      * Set the view for the mail message.
      *
@@ -129,4 +136,19 @@ public function data()
     {
         return array_merge($this->toArray(), $this->viewData);
     }
+
+    /**
+     * Set the priority of this message.
+     *
+     * The value is an integer where 1 is the highest priority and 5 is the lowest.
+     *
+     * @param  int  $level
+     * @return $this
+     */
+    public function priority($level)
+    {
+        $this->priority = $level;
+
+        return $this;
+    }
 }

tests/Notifications/NotificationMailChannelTest.php

@@ -211,6 +211,37 @@ public function testMessageWithToAddress()
         $channel->send($notifiable, $notification);
     }
 
+    public function testMessageWithPriority()
+    {
+        $notification = new NotificationMailChannelTestNotificationWithPriority;
+        $notifiable = new NotificationMailChannelTestNotifiable;
+
+        $message = $notification->toMail($notifiable);
+        $data = $message->toArray();
+
+        $channel = new Illuminate\Notifications\Channels\MailChannel(
+            $mailer = Mockery::mock(Illuminate\Contracts\Mail\Mailer::class)
+        );
+
+        $views = ['notifications::email', 'notifications::email-plain'];
+
+        $mailer->shouldReceive('send')->with($views, $data, Mockery::on(function ($closure) {
+            $mock = Mockery::mock('Illuminate\Mailer\Message');
+
+            $mock->shouldReceive('subject')->once();
+
+            $mock->shouldReceive('to')->once()->with('taylor@laravel.com');
+
+            $mock->shouldReceive('setPriority')->once()->with(1);
+
+            $closure($mock);
+
+            return true;
+        }));
+
+        $channel->send($notifiable, $notification);
+    }
+
     public function testMessageWithMailableContract()
     {
         $notification = new NotificationMailChannelTestNotificationWithMailableContract;
@@ -287,6 +318,15 @@ public function toMail($notifiable)
     }
 }
 
+class NotificationMailChannelTestNotificationWithPriority extends Notification
+{
+    public function toMail($notifiable)
+    {
+        return (new MailMessage)
+            ->priority(1);
+    }
+}
+
 class NotificationMailChannelTestNotificationWithMailableContract extends Notification
 {
     public function toMail($notifiable)