Amber sits in the tcpserver chain for qmail and
implements an "amber list" for incoming mail. This
neither accepts nor rejects connections, but
implements a number of timing-related tricks to
fake out spam and virus software that doesn't
implement SMTP correctly. For example, it can
defer requests from new IP addresses for a few
minutes before it starts passing connections on to
smtpd, pause and check for programs that send data
before the HELO, and otherwise make things rough
for bandit bulk mailers.
