How to add headers to email in Laravel 5.1

I know this is an old post, but I'm passing by the same problem right now and I think this could be useful to others.

If you're using a structure exactly as shown in Laravel (6.x and 7.x), like this:

/**
 * Build the message.
 *
 * @return $this
 */
public function build()
{
    return $this->from('[email protected]')
                ->view('emails.orders.shipped');
}

you could add headers to the E-mail in the format below:

public function build()
{
   return $this->from('[email protected]')
                ->view('emails.orders.shipped')
                ->withSwiftMessage(function ($message) {
                    $message->getHeaders()
                        ->addTextHeader('Custom-Header', 'HeaderValue');
                });
}

I hope this could be useful.

link to the current documentation:https://laravel.com/docs/7.x/mail#customizing-the-swiftmailer-message

Slight modification to @maxim-lanin's answer. You can use it like this, fluently.

\Mail::send('email.view', ['user' => $user], function ($message) use ($user) {
    $message->to($user->email, $user->name)
        ->subject('your message')
        ->getSwiftMessage()
        ->getHeaders()
        ->addTextHeader('x-mailgun-native-send', 'true');
});

Laravel uses SwiftMailer for mail sending.

When you use Mail facade to send an email, you call send() method and define a callback:

\Mail::send('emails.reminder', ['user' => $user], function ($m) use ($user) {
    $m->to($user->email, $user->name)->subject('Your Reminder!');
});

Callback receives $m variable that is an \Illuminate\Mail\Message object, that has getSwiftMessage() method that returns \Swift_Message object which you can use to set headers:

$swiftMessage = $m->getSwiftMessage();

$headers = $swiftMessage->getHeaders();
$headers->addTextHeader('x-mailgun-native-send', 'true');