A few XAMPP configuration points to send the email from PHP by using gmail account, 

1, \xampp\sendmail\sendmail.ini

 smtp_server=smtp.gmail.com

 smtp_port=587

 auth_username=huilin.xiong@gmail.com (your gmail account)

 auth_password=your passowrd


 2, \xampp\php\php.ini

 sendmail_path = "\"D:\PHP\xampp\sendmail\sendmail.exe\" -t"



 3, gmail account sign-in & security setting, 

 set Allow less secure apps: ON

 If this is not set, the sending email will fail.