sending email

bummer

I am having a problem.... but I am not QUIET sure if it is the server or my code.... I am leaning twords the code as there are 3 seperate email functions and 2 are working with no problems.

Anyway, here is what I am using to send:

case "sendmail":
 $id=stripslashes($_POST['id']);
 $msg=stripslashes($_POST['S1']);
 $sub=stripslashes($_POST['subject']);
 $msg=str_replace("\n","<br>",$msg);


 //if (strtolower($id) == "all")
   // { 
	 $sql="select * from `".$ext."_members`";
	 $res=mysql_query($sql);

	$hhh="From: $adName <$adEmail>\nX-Mailer: php (".$_SERVER['REMOTE_ADDR'].")\nContent-Type: text/html;";
	 while($data=mysql_fetch_array($res))
	     {
          $message=str_replace("{name}",$data[member],$msg);
		  $subject=str_replace("{name}",$data[member],$sub);
		   if (isset($data[email]))
		   { 
		   mail($data[email],"$subject","$message",$hhh);
		   }
	 }

 /*else{
  	 $sql="select * from `".$ext."_members` where member='$id'";

	 $res=mysql_query($sql);$data=mysql_fetch_array($res);
	 if ($test=mysql_num_rows($res)==0){ echo"member doesnt exist!"; exit;}
     $msg=str_replace("{name}",$data[member],$msg);
     $sub=str_replace("{name}",$data[member],$sub);

	 $hhh="From: $adName <$adEmail>\nX-Mailer: php (".$_SERVER['REMOTE_ADDR'].")\nContent-Type: text/html;";

		   if (isset($data[email]))
		   { 
		  $res=mail($data[email],"$sub","$msg",$hhh);

		  if (!$res){echo"not sent!";  }
		   }
		   else echo"Invaild email ".$data[email];
 }*/

THAT SENDS OK................
But this is hit and miss... maybe 2 out of 20 have actaully went through

$url="http://".$SERVER[HTTP_HOST].$SERVER[PHP_SELF]."?teacher=$ext";
$url=str_replace("main.php","students.php",$url);
$hhh="From: $adName <$adEmail>\nX-Mailer: php (".$_SERVER['REMOTE_ADDR'].")\nContent-Type: text/html;";
while($data=mysql_fetch_array($res))
{
$message="Dear $data[member]:

$adName has made an update to the school page.

Click on the link below to login and see the changes: 
<a href=$url>$url</a>

";
if (isset($data[email]))
{
mail($data[email],"Page is updated","$message",$hhh);
}
// if ()
}