Pre-requisites: XAMPP  version which includes the sendmail program.

Following example will work fine with XAMPP 1.7.3 release. Please follow the steps below:

STEP 1
Go to php.ini and uncomment following line:
sendmail_path = "\"C:\xampp\sendmail\sendmail.exe\" -t"

STEP 2
1. Go to folder: C:\xampp\sendmail

2. Open sendmail.ini

3.Add following lines:
# A freemail service
account Gmail
tls on
tls_certcheck off
host smtp.gmail.com
from <username>@gmail.com
auth on
user <username>@gmail.com
password <your gmail password>

4. Edit following line at end:
# Set a default account
account default : Gmail

STEP 3
Restart Apache Server

STEP 4
Make test file sendMail.php :

<?php
// The message
$message = "Line 1\nLine 2\nLine 3";

// In case any of our lines are larger than 70 characters, we should use wordwrap()
$message = wordwrap($message, 70);

// Send
if(mail('<username>@<someDomain>.com', 'My Subject', $message))
    echo "Mail sent successfully";
?>

STEP 5
Run sendMail.php in browser e.g. http://localhost/sendMail.php

STEP 6
Check mail at <username>@<someDomain>.com