when the user name is written in Korean, the mail is not sent.

Hi,

Make sure your configuration is made properly and keep testing, I could not say what is the problem exactly. The theme itself has no email options, it does not send emails or has any settings for mailing. You will have to manage these either through the hosting if they provide such a service, or with a plugin
– http://www.wpbeginner.com/wp-tutorials/how-to-use-smtp-server-to-send-wordpress-emails/
– http://webcraft.tools/simple-smtp-plugins-for-wordpress/

Thanks