There are two ways to solve this issue.
1. Change the protocol in app/config/email.php
--> smtp to mail
2. Add the below code, where you disable SSL which is fine in a testing environment and not in a production environment. (Working in laravel 5.1,5.2,5.4,5.5,5.7,5.8)
'stream' => [
'ssl' => [
'allow_self_signed' => true,
'verify_peer' => false,
'verify_peer_name' => false,
],
],