Try using double quotes :
$subject = "You got mail";
$message = "This is one line.\n" .
"This is another.";
mail('your@email.com', $subject, $message);
Single quote do not interpret the content of the string and display it as it is. To do so, you must use double quotes.
A more complete answer : What is the difference between single-quoted and double-quoted strings in PHP?