Please verify below steps for troubleshooting the issue:
You have entered From Name & From Email in the email notification settings of the plugin. You have installed any SMTP plugin to send emails from website. Please note, if you have not installed SMTP plugin to send emails, mail() function does not guaranty you to deliver emails. There are many popular free SMTP plugins available on wordpress.org. We recommend Post SMTP Mailer plugin. Try sending test emails in SMTP plugin to confirm emails are sending correctly. SupportCandy email notification recipients correctly set for all notifications. Also, check if you have applied conditions in the email notification template and they are correct.