I am on PHP 5.60 and the email is set up to send through PHP.
I tried to create a user but it says that "Email failed" to send, after creating the user. Likewise, whenever someone submits a survey, no email is being sent to administrator with the detailed result.
I have enabled debug in config, but I have no idea how to view it. Any ideas?
It depends on your server. It is not unusal that the mail() function via PHP is disabled by the administrator of the server. You will have to ask your hosting company or admin about that.
Meanwhile you can switch using SMTP instead of PHP mail(), which is often the better way. Create a emailaccount for limesurvey and enter the credentials into limesurvey to use that mailaccount for distributing mails.