Just to throw my 2-cents worth in...
If the other (receiving) domain is using an MX record value that is a
CNAME, this error can show... in such a case, this is not a name
resolver error, but rather a DNS error.
It is a violation of the RFCs for the MX record value to resolve to
anything BUT an A record.
I have recommended these sites before, but as a mail admin, checking out
the settings of the OTHER domain when delivery problems are being
reported is just a smart idea.
*intodns.com* - checks a wide variety of DNS issues, including MX
records
*mxtoolbox.com* - has a wide variety of tests available, including
SMTP connection tests. Many of these tests will FAIL if the MX
record for the domain is a CNAME
Good luck to you!
Dan McAllister
IT4SOHO
QMT DNS/Mirror Admin
