Laravel - Mail - Customizing The Swiftmailer Message

The withSwiftMessage method of the Mailable base class allows you to register a closure which will be invoked with the SwiftMailer message instance before sending the message. This gives you an opportunity to deeply customize the message before it is delivered:

    
    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
        $this->view('emails.orders.shipped');
    
        $this->withSwiftMessage(function ($message) {
            $message->getHeaders()->addTextHeader(
                'Custom-Header', 'Header Value'
            );
        });
    
        return $this;
    }