Re: Advanced tricks I use to get rid of spam using MX 4xx

[Harald Hanche-Olsen <hanche@math.ntnu.no>]

+ Marc Perkel <marc@perkel.com>:

| No - on my system a 4xx error only means that that particular server
| isn't ready. It means try the other servers or come back later.

In that case, it would probably be better to just stop listening on
the smtp port while the load is too high.  But you want to tailor your
response to what host is connecting: Too bad then that unix doesn't
let you move such decisions into userland.  If you're listening on a
port, you accept all incoming connections no matter what, and then the
best you can do is either just drop the connection, or try to tell the
client to go away, and this is where you clash with established
protocol.

Are there Unix variants that will let you decide in userland what to
do about an incoming SYN?  The Hurd perhaps?  AFAIK, one of the design
goals of the Hurd is precisely to move stuff from the kernel into
userland.

- Harald