Description:
------------
PHP version: 4.3.8-2.1 

I am emailing the results of a form...
it always looks like it succeeds...
If I put in my yahoo account, it shows up right away.
If I put in the address it needs to go to, it never shows up 
there.
If I send a test from my yahoo account to the address it needs 
to go to, it shows up right away.
I also tested the form to another address - no email shows up.
I tested again to my yahoo account, shows up immediately.
Why would the email succeed to some addresses and not others?
FYI, the FROM address is valid.


Reproduce code:
---------------
<?
if(!empty($_POST)) extract($_POST);
function param($Name, $http_vars)
      {  global $HTTP_POST_VARS;         
       if(isset($HTTP_POST_VARS[$Name]))
         return($HTTP_POST_VARS[$Name]);         
         return("");
         }
if ($Sign_Me_Up == "")
	{$Sign_Me_Up="No";}
	else
	$Sign_Me_Up="Yes, $Sign_Me_Up";
$from = "email@domain.com";
$to = "email@domain.com";
$subject = "request - destination: $PopularDestinations";
$body = "Source = $source\r\n
First Name = $First_Name\r\n
etc...";

if($from != "" && $to != "" && $subject != "")
  {
  $headers = "From: " . $from . "\n" .
             "To: " . $to . "\n" .
             "CC: " . $cc . "\n" .
             "BCC: " . $bcc;     
  $formsent= mail("", $subject, $body, $headers);
  if ($formsent == 1)
  	{
	print("Thank you for your request, we will respond to you shortly.");
	}
	else
	print("I'm sorry, there's a problem with your form. Please try again.");
  }
?>



Expected result:
----------------
I expect to get the Thank You statement and receive the email

Actual result:
--------------
email works only for some addresses.