# 21.18. `smtpd` — SMTP 服务器

源代码: Lib/smtpd.py

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

参见

The aiosmtpd package is a recommended replacement for this module. It is based on `asyncio` and provides a more straightforward API. `smtpd` should be considered deprecated.

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 and RFC 6531 SMTPUTF8 extensions.

## 21.18.1. SMTPServer 对象

class `smtpd.``SMTPServer`(localaddr, remoteaddr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=False)

  Create a new `SMTPServer` object, which binds to local address localaddr. It will treat remoteaddr as an upstream SMTP relayer. Both localaddr and remoteaddr should be a (host, port) tuple. The object 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.

  map is the socket map to use for connections (an initially empty dictionary is a suitable value). If not specified the `asyncore` global socket map is used.

  enable_SMTPUTF8 determines whether the `SMTPUTF8` extension (as defined in RFC 6531) should be enabled. The default is `False`. When `True`, `SMTPUTF8` is accepted as a parameter to the `MAIL` command and when present is passed to `process_message()` in the `kwargs['mail_options']` list. decode_data and enable_SMTPUTF8 cannot be set to `True` at the same time.

  decode_data specifies whether the data portion of the SMTP transaction should be decoded using UTF-8. When decode_data is `False` (the default), the server advertises the `8BITMIME` extension (RFC 6152), accepts the `BODY=8BITMIME` parameter to the `MAIL` command, and when present passes it to `process_message()` in the `kwargs['mail_options']` list. decode_data and enable_SMTPUTF8 cannot be set to `True` at the same time.

  `process_message`(peer, mailfrom, rcpttos, data, **kwargs)

    Raise a `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 5321 format).

    If the decode_data constructor keyword is set to `True`, the data argument will be a unicode string. If it is set to `False`, it will be a bytes object.

    kwargs is a dictionary containing additional information. It is empty if `decode_data=True` was given as an init argument, otherwise it contains the following keys:

    > mail_options:

    >   a list of all received parameters to the `MAIL` command (the elements are uppercase strings; example: `['BODY=8BITMIME', 'SMTPUTF8']`).

    > rcpt_options:

    >   same as mail_options but for the `RCPT` command. Currently no `RCPT TO` options are supported, so for now this will always be an empty list.

    Implementations of `process_message` should use the `**kwargs` signature to accept arbitrary keyword arguments, since future feature enhancements may add keys to the kwargs dictionary.

    Return `None` to request a normal `250 Ok` response; otherwise return the desired response string in RFC 5321 format.

  `channel_class`

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

  3.4 新版功能: The map constructor argument.

  在 3.5 版更改: localaddr and remoteaddr may now contain IPv6 addresses.

  3.5 新版功能: The decode_data and enable_SMTPUTF8 constructor parameters, and the kwargs parameter to `process_message()` when decode_data is `False`.

  在 3.6 版更改: decode_data is now `False` by default.

## 21.18.2. DebuggingServer 对象

class `smtpd.``DebuggingServer`(localaddr, remoteaddr)

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

## 21.18.3. PureProxy对象

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.

## 21.18.4. MailmanProxy 对象

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.

## 21.18.5. SMTPChannel 对象

class `smtpd.``SMTPChannel`(server, conn, addr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=False)

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

  conn and addr are as per the instance variables described below.

  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.

  enable_SMTPUTF8 determines whether the `SMTPUTF8` extension (as defined in RFC 6531) should be enabled. The default is `False`. decode_data and enable_SMTPUTF8 cannot be set to `True` at the same time.

  A dictionary can be specified in map to avoid using a global socket map.

  decode_data specifies whether the data portion of the SMTP transaction should be decoded using UTF-8. The default is `False`. decode_data and enable_SMTPUTF8 cannot be set to `True` at the same time.

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

  在 3.5 版更改: The decode_data and enable_SMTPUTF8 parameters were added.

  在 3.6 版更改: decode_data is now `False` by default.

  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):

  命令 | 所采取的行动
  --- | ---
  HELO | 接受来自客户端的问候语，并将其存储在 `seen_greeting` 中。将服务器设置为基本命令模式。
  EHLO | 接受来自客户的问候并将其存储在 `seen_greeting` 中。将服务器设置为扩展命令模式。
  NOOP | 不采取任何措施。
  QUIT | 干净地关闭连接。
  MAIL | Accepts the “MAIL FROM:” syntax and stores the supplied address as `mailfrom`. In extended command mode, accepts the RFC 1870 SIZE attribute and responds appropriately based on the value of data_size_limit.
  RCPT | Accepts the “RCPT TO:” syntax and stores the supplied addresses in the `rcpttos` list.
  RSET | 重置 `mailfrom`, `rcpttos`, 和 `received_data` ，但不重置问候语。
  DATA | Sets the internal state to `DATA` and stores remaining lines from the client in `received_data` until the terminator `"\r\n.\r\n"` is received.
  HELP | 返回有关命令语法的最少信息
  VRFY | 返回代码252（服务器不知道该地址是否有效）
  EXPN | 报告该命令未实现。