$from_email = 'mailer@server.com';
$to_email = $seller->user_email;
$headers = "From: FROM NAME <$from_email>" . "\r\n";
$msg = "Ovo je poruka sa WP servera";
$subject = "WP mail subject";
$attachments = 'neki_file';
wp_mail($to_email, $subject, $msg, $headers, $attachments);