are double bounces from a system that is an MX secondary. The
bounces are for spam that was accepted by the secondary, refused
by the primary, and cannot be returned to the spammer. Even the
most non-network oriented single-ended filter would benefit from
protocols that coordinate MX secondaries.
...
You can make secondary mail server know valid addresses in the domain
In the real world, that is wrong. Only when the MX secondaries are
either unneeded or practically the same computer as the MX primary
can you hope to have a common list of valid addresses. The rest of
the time, there are compelling practical and policy reasons that keep
MX secondaries from having a common and complete list of valid addresses.
Moreover, this is entirely irrelevant to problem mentioned.
and reject the remaining.
Such solutions for sendmail have been discussed a few times in
news:comp.mail.sendmail :
a) virtusertable for non local email domains
That is irrelevant to the problem I'm talking about as well as not
useful for the problem you are talking about.
b) LDAP based routing [FEATURE(`ldap_routing')]
Thaty is irrelevant to the problem I'm talking about as well as
a doubtful solution for the problem you are talking about.
If you need more details ask on news:comp.mail.sendmail
A newsgroup is rarely my first suggestion for technical information,
particularly in a forum where contributors should be expected to know
far more about the topic than the vast majority of contributors to
newsgroups. Far better sources for information about sendmail include
the sendmail "ops" document, the cf/README file, the sendmail source,
and the many web pages at http://www.sendmail.org.
I suggest to change wording of the recommendation because I also think
that secondary that accept message to invalid address in the domain is
not a good idea.
Please re-read what I wrote and consider the context. The reason the
primary MX server rejects the messages that have come through the
secondary MX server is that they fail either DCC or sendmail access_DB
filtering. The target addresses are entirely valid. The invalid
addresses are the nominal senders of the spam.
Vernon Schryver vjs(_at_)rhyolite(_dot_)com
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