Milter-greylist

I wrote:
>> One more note on tarpitting:  the full-on implementation is
>> actually that of a connection throttle; traffic is let through
>> very very slowly.  The idea of pausing often accomplishes the
>> same thing, but it's easily interpreted as a lost connection.

Bob Friesenhahn wrote:
> It seems like this makes your server susceptible to DOS.

If you don't have a hard connection rate throttle, you are correct.
http://www.acme.com/mail_filtering/sendmail_config.html (as referenced
in my previous email) has some good tips on that.

> It also assumes that the bots are implemented well and will sever
> slow connections.

Please refer to http://mailchannels.com/images/drop-off.png (also in
my last email), which uses Spamhaus data to prove that assumption.
More to the point, 500 seconds is enough time for the connection to be
severed, which is far less than the typical greylisting delay time.