XAMPP should have come with a "fake" sendmail program. In that case, you can use sendmail as well:
[mail function]
; For Win32 only.
; http://php.net/smtp
;SMTP = localhost
; http://php.net/smtp-port
;smtp_port = 25
; For Win32 only.
; http://php.net/sendmail-from
;sendmail_from = me@example.com
; For Unix only. You may supply arguments as well (default: "sendmail -t -i").
; http://php.net/sendmail-path
sendmail_path = "C:/xampp/sendmail/sendmail.exe -t -i"
Sendmail should have a sendmail.ini
with it; it should be configured as so:
# Example for a user configuration file
# Set default values for all following accounts.
defaults
logfile "C:\xampp\sendmail\sendmail.log"
# Mercury
#account Mercury
#host localhost
#from postmaster@localhost
#auth off
# A freemail service example
account ACCOUNTNAME_HERE
tls on
tls_certcheck off
host smtp.gmail.com
from EMAIL_HERE
auth on
user EMAIL_HERE
password PASSWORD_HERE
# Set a default account
account default : ACCOUNTNAME_HERE
Of course, replace ACCOUNTNAME_HERE with an arbitrary account name, replace EMAIL_HERE with a valid email (such as a Gmail or Hotmail), and replace PASSWORD_HERE with the password to your email. Now, you should be able to send mail. Remember to restart Apache (from the control panel or the batch files) to allow the changes to PHP to work.