If you are attempting to configure xampp to send real email over the internet, you are invariably direct to make setting changes in sendmail.ini
which is in the sendmail folder but when you look in xampp you may not see a sendmail
folder.
To fix this error you need to download sendmail for xampp which is the sendmail folder and all the required files.
To download sendmail so you can send mail from within xampp ...
sendmail
folder to clipboard.sendmail
folder and double click it to open it.Although sendmail is no longer being developed or updated, sendmail works as is. You can read more about sendmail here.