$homeID = "DonVito:";

if ( strpos( $postcontent, $homeID ) === 0 ){
    header("location:result.php?p=$postcontent&mail=Sent");
}
else{
//redirect back to site
header("location:result.php?p=$postcontent&debug=noMailSent");
}

<?php
$host="localhost"; // Host name
$username="****"; // Mysql username
$password="***"; // Mysql password
$db_name="*******"; // Database name
$tbl_name="post";

$_POST['myusername']

if($count==1){
//Create cookie
    $hour = time()+3600;
    header("location:index.php");
    setcookie('ID_group_planner', $_POST['myusername'], $hour);
    setcookie('Key_group_planner', $_POST['mypassword'], $hour);
}
else {
header("location:index.php?login_error=1");
}