21.18. smtpd — SMTP 服务器

源代码: Lib/smtpd.py

---

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

也參考

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=True)

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. If set to True, decode_data must be False (otherwise an error is raised). 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 specifies whether the data portion of the SMTP transaction should be decoded using UTF-8. The default is True for backward compatibility reasons, but will change to False in Python 3.6; specify the keyword value explicitly to avoid the DeprecationWarning. When decode_data is set to False 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.

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 unless at least one of decode_data=False or enable_SMTPUTF8=True was given as an init parameter, in which case 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 版新加入: The map constructor argument.

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

3.5 版新加入: the decode_data and enable_SMTPUTF8 constructor arguments, and the kwargs argument to process_message() when one or more of these is specified.

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=True)

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. A ValueError is raised if both enable_SMTPUTF8 and decode_data are 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 True for backward compatibility reasons, but will change to False in Python 3.6. Specify the keyword value explicitly to avoid the DeprecationWarning.

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

3.5 版更變: the decode_data and enable_SMTPUTF8 arguments were added.

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。