PHP код:
$filename = "codes.gif";
$fd = fopen($filename, "rb");
$size = filesize($filename);
$data = fread($fd, $size);
fclose($fd);
$boundary = "_" . md5(uniqid(time()));
$header = "\nMIME-Version: 1.0\nContent-Type: multipart/mixed; boundary=\"$boundary\"\nContent-Transfer-Encoding: 7bit";
$multipart = "This is a MIME Encoded Message\n\n";
$multipart .= "--$boundary\n";
$multipart .= "Content-Type: image.gif\n";
$multipart .= "Content-Disposition: attachment; filename=\"$filename\"\n";
$multipart .= "Content-Transfer-Encoding: base64\n\n";
$multipart .= chunk_split(base64_encode($data));
$multipart .= "--$boundary--\n";
@mail($mail_to, "Test", $multipart, "From: ".$mail_from.$header);
только что проверил - работает