I have Google’d around asked a lot of smart people and still can’t come up with a solid answer. More specifically, the question I have is:
Why, when sending emails to certain domains, do I get the error: 451 Could not load DRD for domain
Because I deal with fairly large mailing lists, I see odd errors a lot. Most of them I can disregard. In any case in which I see an error over 1,000 times, I make it a policy to deal with it. I have seen one close to 9 million.
It appears to be an error from a Symantec appliance, but people write about it coming from Exchange servers as well.
If anyone has any idea what this, please email me, leave a comment, or post a link to somewhere.

DRD is a new DNS entry for redirecting domains. In case you want to change your domain name, you would create a DRD entry on the old domain indicating that all inquires to the old domain would be replaced by the new domain name. Thus http://www.olddomain.com forwards a request to http://www.newdomain.com.
Since the standard is pretty new, not all software supports it.
RFC 2672 (Proposed Standard)
Non-Terminal DNS Name Redirection by M. Crawford
Defines DNAME record, which maps a subtree of the DNS to another domain: like a more general form of CNAME.
Aug-1999
@Jeff I don’t think that is the same DRD. Even if is it, that still begs the question, why am I getting that error from a bounced mail message? Ie what does it have to do with email delivery?
you receiving an error because your software do not have support of drd
I am using Postfix. What does supporting a DRD actually change?
you receiving an error because your software do not have support of drd
I am using Postfix. What does supporting a DRD actually change?
Did you ever find a fix for this? I use MDaemon
I didn't find a fix for this. I kind of gave up for the time being. I am still open to hearing results though.