[Mimedefang] Only MX record is fake

dfs at roaringpenguin.com dfs at roaringpenguin.com
Thu Nov 17 16:05:16 EST 2011

> Those people checking for valid MX records for a sender's domain from
> within MIMEdefang ... is anybody checking if a sender's one and only MX
> record is a fake MX tempfailing service? Has anyone ever seen this type
> of setup for legitimate e-mail?

Our commercial product has a setting to reject mail from any domain
that has an MX record that resolves back to or ::1.  We've
had no false-positives reported.

A more aggressive setting also rejects mail from domains with MX records
in RFC 1918 private address space and non-unicast addresses.  Believe it or
not, there are some domains that have MX records resolving to
(but other MX records that really are routable) so you may get some FPs if
you use the more aggressive approach.



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