源代码： Lib/smtpd.py
This module offers several classes to implement SMTP servers. One is a generic do-nothing implementation, which can be overridden, while the other two offer specific mail-sending strategies.
创建新的 SMTPServer 对象，绑定到本地地址 localaddr 。它将视 remoteaddr as an upstream SMTP relayer. It inherits from asyncore.dispatcher ，且因此将自身插入 asyncore ‘s event loop on instantiation.
引发 NotImplementedError exception. Override this in subclasses to do something useful with this message. Whatever was passed in the constructor as remoteaddr will be available as the _remoteaddr 属性。 peer 是远程主机的地址， mailfrom 是信封发起人， rcpttos are the envelope recipients and data is a string containing the contents of the e-mail (which should be in RFC 2822 格式)。
Create a new debugging server. Arguments are as per SMTPServer . Messages will be discarded, and printed on stdout.
Create a new pure proxy server. Arguments are as per SMTPServer . Everything will be relayed to remoteaddr . Note that running this has a good chance to make you into an open relay, so please be careful.
Create a new pure proxy server. Arguments are as per SMTPServer . Everything will be relayed to remoteaddr , unless local mailman configurations knows about an address, in which case it will be handled via mailman. Note that running this has a good chance to make you into an open relay, so please be careful.
