Вы должны перенаправить на другой php-файл и передать параметр по URL. Пример:
sendemail.php
<?php
/** After send the email, check what kind form is (I don't know how do you check this).
This example is just to show you: */
if ($formType == 'review') {
$type = 'review';
} else if ($formType == 'anothertype') {
$type = 'anothertype';
}
header('Location: /thankspage.php?type=' . $type);
?>
thankspage.php
<?php
$type = $_GET['type'];
if ($type == 'review') {
echo '<h1>Thanks for your review</h1>';
} else if($type == 'anothertype') {
echo '<h1>Thanks for your anothertype</h1>';
}
?>