big message to gmail

Could somebody please help me with this attachments code, as it doesn't send to gmail big messages (>500KB):

$email_to = "somebody@gmail.com"; // Who the email is to

$headers = "From: ".$name_from." <".$email_from.">"."\r\n";
$headers .= "Reply-To: ".$name_from." <".$email_from.">"."\r\n";

$semi_rand = md5(time());
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";
$semi_rand2 = md5(time());
$mime_boundary2 = "==Multipart_Boundary_x{$semi_rand2}x";

$headers .= "\nMIME-Version: 1.0\n" .
"Content-Type: multipart/mixed;\n" .
" boundary=\"{$mime_boundary}\"";

$email_message .= "--{$mime_boundary}\n";
$email_message .= "Content-Type:text/plain; charset=UTF-8\n";
$email_message .= "Content-Transfer-Encoding: 7bit\n\n";
$email_message .= $email_txt ."\n";


if ($files != ""){

$fileatt_type = "application/octet-stream"; // File Type
$files_array = explode(",",$files);
$no_files = count($files_array)-1;
for ($a = 0; $a <$no_files; $a++) {

$fileatt = "files/".$files_array[$a]; // Path to the file

$file = fopen($fileatt,'rb');
$data = fread($file,filesize($fileatt));
fclose($file);
$data = chunk_split(base64_encode($data));

$email_message .= "--{$mime_boundary2}\n";
$email_message .= "Content-Type: {$fileatt_type}; name=\"{$files_array[$a]}\"\n";
$email_message .= "Content-Disposition: attachment; filename=\"{$files_array[$a]}\"\n";
$email_message .= "Content-Transfer-Encoding: base64\n\n";
$email_message .= $data . "\n\n";

}};
$email_message .="--{$mime_boundary}--\n";

$ok = @mail($email_to, $email_subject, $email_message, $headers);
if ($files != ""){for ($a = 0; $a <$no_files; $a++) {unlink("files/".$files_array[$a]);};};