Python milter 介绍
这是 Python 的 milter 模块，提供了 Sendmail 的
libmilter 的 Python 接口。
Milters can run on the same machine as sendmail, or another machine. The
milter can even run with a different operating system or processor than
sendmail. Sendmail talks to the milter via a local or internet socket, and
keeps the milter informed of events as it processes a mail connection. At any
point, the milter can cut the conversation short by telling sendmail to
ACCEPT, REJECT, or DISCARD the message. After receiving a complete message
from sendmail, the milter can again REJECT or DISCARD it, but it can also
ACCEPT it with changes to the headers or body.