Enable a CentOS 7(LAMPP & Laravel) server send email via SSL

I have a CentOS 7 server running lampp, with domain name xxx.example.com. I have successfully config the SSL certificate for https://xxx.example.com.

For email notification purpose, I need to send some emails. My smtp server's domain is smtp.example.com. I could send email in my local environment (Windows 10, xampp) with SSL activated. But when I deploy the site on CentOS, it can't send email with SSL option activated. I have to bypass the SSL verification part to send the email:

 'stream' => [
     'ssl' => [
            'allow_self_signed' => true,
            'verify_peer' => false,
            'verify_peer_name' => false,
      ],
  ],

So, how should I set up my CentOS environment to send email with SSL correctly?