Frank Ellermann wrote:
You especially don't want an "accept everything" policy on the
lowest-priority MX because spammers do expect and exploit that.
(Hmm, is that another recommendation that should go into the RFC if
it isn't already there? "If there are multiple MX for a domain, they
SHOULD implement the same policy for accepting or rejecting mail. In
particular, a lower priority MX should not accept mail that a higher
priority MX rejects")
Yes, but I'd say "for MXs with a different priority the MX with the
numerically higher priority SHOULD be at least as restrictive with
respect to accepting mails for the domain in question as the MX with
the numerically lower priority."
Here is a MX version of "GreyListing," that was getting some interesting
positive results from some of our sysops who tried it:
http://www.joreybump.com/code/howto/nolisting.html
Note: I'm not endorsing it, nor do I know how spread the usage is. Its
just caught my attention when its as discussed in our anti-spam support
forum.
--
HLS