On Wed, 14 Jan 2009 14:28:54 EST, Paul Russell said:

> This error message is indicative of a DNS problem of some sort.  The fact
> that only charter.net subscribers seem to be affected indicates that the
> problem is probably in the charter.net DNS infrastructure.
>
> The server which rejected the message is apparently configured to validate
> the domain portion of the envelope-sender (return-path) address and reject
> any message where the sender domain does not resolve in DNS.  This technique
> effectively results in the rejection of a great deal of spam and malware with
> completely bogus sender addresses, however, it can result in the rejection of
> messages from valid domains, if there are DNS problems.

Which is why *clued* admins always use 4xx reject codes for DNS tempfails, and
only return a 5XX if they get back an *authoritative* NXDOMAIN.
However, I have ceasde to be amazed at the lack of clue I keep seeing from
companies that really should know better...