Robert Penz writes:
It's a war of attrition. There's not much that can be done except to keepscaling up the system to cope with the load. It's not only SMTP, for example. DNS server operators, for example, often have no choice but overprovision their bandwidth and CPU to deal with attacks on DNSservers. hmmm ... I would think that if the SMTP connection is handled by a program which does not create a process or thread for each handshake before it has
Except that you will wind up with a system design that now has to use a single process to handle all SMTP connections. That would be how things get done on Windows, and we've evolved a bit way beyond that.
done a DNS RBL check it would increase the systems resistance to spam waves
Except that dropping a connection at this point has proven not to work, as soon as you run into a real mail server, but a broken one that interprets an immediately disconnected connection as an invitation to reconnect immediately.
Can courier not just drop it?
And watch your bandwidth get eaten up by a broken server that's trying to dump on you a load of spam, using multiple connections which immediatly try to reconnect as soon as you drop them.
The most reliable way to reject unwanted mail is by RCPT TO. This is why even when it's a blacklisted sender, it doesn't get rejected until it actually sends an RCPT TO. Which means that you have to fully implement SMTP up to that point.
This means that you'll wind up with a model of using a monolithic, huge process for all SMTP connections, or a single lightweight process per connection.
But if you really want to try to see what happens if you just drop a blacklisted connection, it's fairly easy to hack it into courieresmtpd's main(). Just check the BLOCK environment variable, and terminate immediately if it is set.
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