I have installed openDKIM on Postfix. I have the latest updates installed. I am able to sign and verify dkim messages, that is working. However, I am having trouble getting the x= expiration tag added to each signed message. I have added the SignatureTTL value in opendkim.conf which is what I thought should add the x tag, but it is not working. I've tried everything I can think of at this point and I'm wondering if this is a bug?