After every $smtp->methodname() call, add some error checking. Like this:

 $smtp->mail($from) or die $smtp->message();

and then you'll see exactly where your error is. Visual inspection of your code seems correct. It would be more helpful also if you show the actual error message you got *and* where you got it. There is no error reporting in the code you posted, so nobody knows for sure what is happening to you.