php mail issue?

The following is a snippet of code from a php program that sends an email.

      $mailto = "redacted@hotmail.com, sales@redacted.com, kneff@redacted.com";
      $subj = "On-Line Invoice Payment";
      $totpmnt = 0;
      $body = "Customer $custname has made on on-line payment as follows:\n";
      for ($i = 0; $i < $ni; $i++) {
// fix this regarding "blank" invoice #
            if ($paids[$i] != "") {
                  $pdfmt = sprintf($paids[$i]);
                  $body = $body . "Invoice Number: $invnos[$i] - Payment Amount: \$$pdfmt\n";
                  $totpmnt = $totpmnt + $paids[$i];
            }
      }      
      $totf = sprintf("%01.2f", $totpmnt);                  
      $body = $body . "\nThe total amount paid was: \$" . $totf. "\n";
      $header  = "MIME-Version: 1.0\r\n";
      $header .= "Content-type: text/html; charset=iso-8859-1\r\n";
      $header .= "From: donotreply@LSS.com\r\n";      
      $header .= "Cc: redacted@gmail.com\r\n";

      $mres = mail($mailto, $subj, $body, $header);

In a test this AM, I executed this code; I am the Cc at the end of $header. I received the email; see attached.

The recipient kneff@lawnsprinklerservices.com says she received the email; the others did not (they claim).

Subsequent to that, I manually composed an email to the 3 emails in the $mailto variable. It was received by all.

Is there anything wrong with the formatting that could be causing this failure?

Thanks
Payment-email.jpg