On Tue, Mar 09, 2004 at 06:07:36PM +0000, David Woodhouse wrote:
MX backup but where the primary is _actually_ currently down and cannot
immediately deny the existence of the recipient address. Obviously I
have to accept the mail in the case of temporary failures to contact the
primary -- that's what MX backup is all about, after all.
My experiments have shown that at least some spammers treat all MX records as
having equal weight, and just pick one at random. Before implementing
greylisting, I had three MX servers, and found that a significant volume of
spam was coming through the other two. After implementing greylisting, I had to
remove the other two MX servers (which were not under my direct control and did
not enable greylisting) in order to allow greylisting to have the greatest
impact.
Sending bounces for messages that have been unconditionally accepted by your
backup MX servers may not be a good idea.
Greg Hewgill
http://hewgill.com