IIS Has No Sendmail so i need to do something with this

function xforum_notifyAboutNewPost($link, $categoryID, $threadID, $userID)
{
$category_object = xforum_getCategoryByID($link, $categoryID);
$thread_object = xforum_getThreadByID($link, $categoryID, $threadID);

$SQLQuery = "SELECT * FROM Category_" . $categoryID;
$SQLQuery .= " WHERE ThreadID=" . $threadID;
$result = mysql_query($SQLQuery, $link);

if ($row_object = mysql_fetch_object($result)) {
if ($row_object->UserID < 0 && abs($row_object->UserID) != $userID) {
$user_object = xforum_getUserByID($link, abs($row_object->UserID));
$sendString = "Someone has posted a reply to your thread:nn";
$sendString .= " " . $thread_object->subject . "nn";
$sendString .= "in the " . $category_object->categoryName . " category at " . _XFORUM_NAME . ".";
mail($user_object->email, "Post Notification", $sendString, "From: " . _XFORUM_ADMIN_EMAIL);
}
}