$headers = "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=koi8-r\r\n";

$to = convert_cyr_string($to, "w", "k");
$from = convert_cyr_string($from, "w", "k");
$headers .= "From: $from\r\n";
$subject = convert_cyr_string($subject, "w", "k");

$body = convert_cyr_string($body, "w", "k");

mail("$to", "$subject", "$body", "$headers");

$headers .= "From: Иванов И.И.<ivanov@mail.server>;\r\n";