John Hinton:
> My goal is to have a Postfix mailserver set up to accept mail for other
> Postfix servers running multiple domains 'if and only if they are not
> accessible'.
What's missing from this picture that not only hosts can fail, but
also networks. Network outages happen all the time in different
parts of the Internet.
As the result of outages in intermediate networks, the primary MX
server will be reachable for most clients but unreachable for others.
Therefore, the secondary MX server will see legitimate connections
while the primary MX server is up.
Secondary MX servers are a source of accept-then-bounce spam when
they don't reject mail with "recipient unknown", and when they don't
enforce the same anti-spam policy as the primary MXen. Such servers
may eventually become blacklisted.
Search the web for backscatter, outscatter, etc.
Wietse
