PHP Email - Should be built in the headers or in the body? (what's more correct)

Question

As I'm working on building and sending email in PHP I've noticed that sometimes people put the code for the message and file attachment in the headers and sometimes in the body. They both work. So what's more correct, or does it make a difference?

Here's example code: In the headers

if (is_uploaded_file($attachment)) {
  $file = fopen($attachment, 'rb');
  $data = fread($file, filesize($attachment));
  fclose($file);

  $data = chunk_split(base64_encode($data));
  $uid = md5(uniqueid(time()));

  $headers = "From: $from\r\n";
  $headers .= "MIME-Version: 1.0\r\n";
  $headers .= "Content-Type: multipart/mixed; boundary=\"{$uid}\"\r\n\r\n";

  $headers .= "--{$uid}\r\n";
  $headers .= "Content-Type: text/plain; charset=\"iso-8859-1\"\r\n\r\n";
  $headers .= $message. "\r\n\r\n";

  $headers .= "--{$uid}\r\n";
  $headers .= Content-Type: {$att_type}; name=\"{$att_type}\"\r\n";
  $headers .= Content-Transfer-Encoding: base64\r\n";
  $headers .= Content-Disposition: attachment; filename=\"{$att_name}\"\r\n\r\n";
  $headers .= $data . "\r\n\r\n";
  $headers .= "--{$uid}--\r\n";
}
  mail($to, $subject, $message, $headers);

Same code in the message (body):

if (is_uploaded_file($attachment)) {
  $file = fopen($attachment, 'rb');
  $data = fread($file, filesize($attachment));
  fclose($file);

  $data = chunk_split(base64_encode($data));
  $uid = md5(uniqueid(time()));

  $headers = "From: $from\r\n";
  $headers .= "MIME-Version: 1.0\r\n";
  $headers .= "Content-Type: multipart/mixed; boundary=\"{$uid}\"\r\n\r\n";

  $message = "This is a multi-part message in MIME format.\r\n";
  $message .= "--{$uid}\r\n";
  $message .= "Content-Type: text/plain; charset=\"iso-8859-1\"\r\n\r\n";
  $message .= $msg. "\r\n\r\n";

  $message .= "\r\n--{$uid}\r\n";
  $message .= Content-Type: {$att_type}; name=\"{$att_type}\"\r\n";
  $message .= Content-Transfer-Encoding: base64\r\n";
  $message .= Content-Disposition: attachment; filename=\"{$att_name}\"\r\n\r\n";
  $message .= $data . "\r\n";
  $message .= "--{$uid}--\r\n";
}
  mail($to, $subject, $message, $headers);

Assuming both of these work, is one method better than the other? When or why does it matter, or does it matter? I can't seem to find an answer to this.

Answer 1

It should be in the body - as per the spec.