[Mimedefang] MX -> 127.0.0.1

[Kevin A. McGrail]

No problem and BTW, in fairness to Net::DNS, I'm not sure the bug for
sorting MX's is in Net::DNS or in my interpretation of the documents but
it's easy enough to sort once the answer is returned.

> Good catches. It was originally coded just to check for existence (so no
> need for priority), with the assumption that I had control over all
> participants' DNS (so no need for the CNAME check). Adding those features
> would certainly make the code more generally useful.