Laravel 5.4 mail messages how to edit header and footer

I already figure it out just change the name of the env file to your App name instead of laravel. This is the sample below.

APP_NAME=Laravel

Change it to

APP_NAME=YOUR_APP_NAME

there is also one way to edit your mail template. Just go to resources/views/vendor/notifications/email.blade.php and you can also edit the message to your mail just go to resources/views/vendor/markdown/message.blade.php

I want to change the header Laravel from my App name and the Hello with a Hello $user->name and the Regards, with my App name also and the footer below to the App name also

Mailable Markdown by default has the config('app.name') that picks the APP_NAME from your .env file. So by modifying the APP_NAME will effect on your markdown template.

OR if you modifying it manually, run the following command on your terminal
php artisan vendor:publish --tag=laravel-mail and go to the resources/views/vendor/mail/html/message.blade.php and modify the header and footer slot.

For changing Hello to Hello {user_name}, there is markdown called greeting() method that holds Hello!, you can change it whatever you want.

For Regards run this command on your terminal
php artisan vendor:publish --tag=laravel-notifications and go to the resources/views/vendor/notifications/email.blade.php and modify the Regards whatever you want.

To know more in details take a look on customizing markdown email.

You are using default component for your email template named @component('mail::message'), It does not allow you to modify header. But if you go to the file of this component,

\vendor\laravel\framework\src\Illuminate\Mail\resources\views\markdown\message.blade.php

you will notice that it uses another component @component('mail::layout'),

Just copy content of message.blade.php file into your .blade.php and replace {{ $slot }} with what you had in your file before.

And you are done.