Expected response code 250 but got an empty response laravel 8

https://blog.trippyboy.com/2021/laravel/laravel-expected-response-code-250-but-got-an-empty-response/

  
./config/mail.php  
  
'local_domain' => env('MAIL_HOST'),  
  
  
'default' => env('MAIL_MAILER', 'smtp'),  
'mailers' => [  
    'smtp' => [  
        'transport' => 'smtp',  
        'host' => env('MAIL_HOST', 'smtp.mailgun.org'),  
        'port' => env('MAIL_PORT', 587),  
        'encryption' => env('MAIL_ENCRYPTION', 'tls'),  
        'username' => env('MAIL_USERNAME'),  
        'password' => env('MAIL_PASSWORD'),  
        'timeout' => null,  
        'auth_mode' => null,  
        'local_domain' => env('MAIL_HOST'),  
],