See what this says:
https://wordpress.org/plugins/check-email/
You may need to install an SMTP plugin to send mail.
Hello,
You can opt for the plugin route as suggested by Steven, in case you wish to debug manual below is what I would suggest.
One thing which I can suggest here is by enabling the error logs. Error logging is the process of tracking and monitoring issues that occur on a website. This is usually done with a record of simple text files that live on your web server and are updated whenever an error occurs. Error logs are used to identify the number of problems that occur, provide details about each one, and show when they took place.
Check this and see if that helps.
Debugging in WordPress
https://wordpress.com/go/tutorials/set-up-wordpress-error-logs/