
"smtpd" --- SMTP Server
***********************

**Source code:** Lib/smtpd.py

======================================================================

This module offers several classes to implement SMTP (email) servers.

Several server implementations are present; one is a generic do-
nothing implementation, which can be overridden, while the other two
offer specific mail-sending strategies.

Additionally the SMTPChannel may be extended to implement very
specific interaction behaviour with SMTP clients.

The code supports **RFC 5321**, plus the **RFC 1870** SIZE extension.


SMTPServer Objects
==================

class class smtpd.SMTPServer(localaddr, remoteaddr, data_size_limit=33554432)

   Create a new "SMTPServer" object, which binds to local address
   *localaddr*.  It will treat *remoteaddr* as an upstream SMTP
   relayer.  It inherits from "asyncore.dispatcher", and so will
   insert itself into "asyncore"'s event loop on instantiation.

   *data_size_limit* specifies the maximum number of bytes that will
   be accepted in a "DATA" command.  A value of "None" or "0" means no
   limit.

   process_message(peer, mailfrom, rcpttos, data)

      Raise "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" attribute. *peer* is the remote host's
      address, *mailfrom* is the envelope originator, *rcpttos* are
      the envelope recipients and *data* is a string containing the
      contents of the e-mail (which should be in **RFC 2822** format).

   channel_class

      Override this in subclasses to use a custom "SMTPChannel" for
      managing SMTP clients.


DebuggingServer Objects
=======================

class class smtpd.DebuggingServer(localaddr, remoteaddr)

   Create a new debugging server.  Arguments are as per "SMTPServer".
   Messages will be discarded, and printed on stdout.


PureProxy Objects
=================

class class smtpd.PureProxy(localaddr, remoteaddr)

   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.


MailmanProxy Objects
====================

class class smtpd.MailmanProxy(localaddr, remoteaddr)

   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.


SMTPChannel Objects
===================

class class smtpd.SMTPChannel(server, conn, addr)

   Create a new "SMTPChannel" object which manages the communication
   between the server and a single SMTP client.

   To use a custom SMTPChannel implementation you need to override the
   "SMTPServer.channel_class" of your "SMTPServer".

   The "SMTPChannel" has the following instance variables:

   smtp_server

      Holds the "SMTPServer" that spawned this channel.

   conn

      Holds the socket object connecting to the client.

   addr

      Holds the address of the client, the second value returned by
      "socket.accept"

   received_lines

      Holds a list of the line strings (decoded using UTF-8) received
      from the client. The lines have their ""\r\n"" line ending
      translated to ""\n"".

   smtp_state

      Holds the current state of the channel. This will be either
      "COMMAND" initially and then "DATA" after the client sends a
      "DATA" line.

   seen_greeting

      Holds a string containing the greeting sent by the client in its
      "HELO".

   mailfrom

      Holds a string containing the address identified in the "MAIL
      FROM:" line from the client.

   rcpttos

      Holds a list of strings containing the addresses identified in
      the "RCPT TO:" lines from the client.

   received_data

      Holds a string containing all of the data sent by the client
      during the DATA state, up to but not including the terminating
      ""\r\n.\r\n"".

   fqdn

      Holds the fully-qualified domain name of the server as returned
      by "socket.getfqdn()".

   peer

      Holds the name of the client peer as returned by
      "conn.getpeername()" where "conn" is "conn".

   The "SMTPChannel" operates by invoking methods named
   "smtp_<command>" upon reception of a command line from the client.
   Built into the base "SMTPChannel" class are methods for handling
   the following commands (and responding to them appropriately):

   +----------+---------------------------------------------------------------------+
   | Command  | Action taken                                                        |
   +==========+=====================================================================+
   | HELO     | Accepts the greeting from the client and stores it in               |
   +----------+---------------------------------------------------------------------+
   | EHLO     | Accepts the greeting from the client and stores it in               |
   +----------+---------------------------------------------------------------------+
   | NOOP     | Takes no action.                                                    |
   +----------+---------------------------------------------------------------------+
   | QUIT     | Closes the connection cleanly.                                      |
   +----------+---------------------------------------------------------------------+
   | MAIL     | Accepts the "MAIL FROM:" syntax and stores the supplied address as  |
   +----------+---------------------------------------------------------------------+
   | RCPT     | Accepts the "RCPT TO:" syntax and stores the supplied addresses in  |
   +----------+---------------------------------------------------------------------+
   | RSET     | Resets the "mailfrom", "rcpttos", and "received_data", but not the  |
   +----------+---------------------------------------------------------------------+
   | DATA     | Sets the internal state to "DATA" and stores remaining lines from   |
   +----------+---------------------------------------------------------------------+
   | HELP     | Returns minimal information on command syntax                       |
   +----------+---------------------------------------------------------------------+
   | VRFY     | Returns code 252 (the server doesn't know if the address is valid)  |
   +----------+---------------------------------------------------------------------+
   | EXPN     | Reports that the command is not implemented.                        |
   +----------+---------------------------------------------------------------------+
