Hello,
We have spamdyke for this...
We both are using kloxo and spamdyke from its begining!
Knowing that we have spamdyke and having configured spamdyke, I have placed the above message as spamdyke has failed.
Investigating the issue, I found that a combination od spamdyke and qmail has a fundamental flaw, which is well known to experts. For many years I thought that. Not anymore, looking at the new spammiing techniques used by spammers in the last weeks on my server. So let me explain you and Mustafa why I have placed this:
When an incoming connection is made from sender/spammer to the server, spamdyke will only check certain parameters of that connection.
One of them is rcphost.Spamdyke fails to check is if an email address exists in the system at all. This means that if a domain exists in rcphost but not the email address, then spamdyke allows that connection.
Qmail does not check
AT THE TIME OF AN INCOMING CONNECTIONif an email address exists. It will first accept an email for processing. That email is delivered in the first place.
Only thereafter Qmail wakes up and finds that the email could not be delivered because the recipients email address does not exists on the server.
Thereafter Qmail sends undelivered to the email address available in the Return-Path.
This is well known and used extensively by spammers.
Spammers use this flaw of Qmail to forge Return-Path != to sender's email address.As a consequence, the undelivered goes to someone who did not send that email.
With this technique, my server became a spamming server. I needed to use firewall to block IP Address of the spammer.
Until I found above mentioned links, I did not really follow what was happening. Since the undelivered is never registered, an Administrator also never notices this abuse of a sever. Now I have read details of the flaw and respective solutions, I this it is neccesary to use more protection against this flaw of qmail.
Spacedust, let me know if I could change something in spamdyke to achieve the solution, if you think I missed something.