<?php
$to = 'test@test.ru';
$subject = 'Тема письма';
$message = 'Текст письма';
if (!empty($_POST['submit'])) {
mail($to, $subject, $message);
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="ru" lang="ru">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title>title</title>
</head>
<body>
<form action="" method="post">
<input type="submit" name="submit" value="Отправить" />
</form>
</body>
</html>
]]>