发送电子邮件与php BCC和To关系以及垃圾邮件问题

i am having a issue with sending emails with cronjobs. actually i need to send email to all the recently joined users and so the emails are something like $to='acx1@xyz.com,acx2@xyz.com,acx3@xyz.com';

here i need to send the mail to all the receipts but not to let them know that i have sent this mail to all these persons in receipt basically BCC them

but the problem is that if i put the $to into BCC then what should i put in to function of mail

if to is empty then it may be spamed

i want to send this mail to all the receipts but when they check the headers they should see their email only

and one more issue please let me know if i am using correct headers ? because sometimes my email is spammed by gmail

   $from='tests.com';
   $to='contact@test.com';
   $message="<body> some html data with inline css </body>"

  $subject="Hii this is test";
  $headers .= 'MIME-Version: 1.0' . "
"; 
  $headers .= 'Content-type: text/html; charset=iso-8859-1'."
";
  $headers .= "From: $from <contact@test.com>" . "
";
  $headers .= "Reply-To: contact@test.com" . "
";
  $headers .= 'BCC:   acx1@xyz.com,acx2@xyz.com,acx3@xyz.com' . "
";
  mail($to, $subject, $message, $headers);