"smtplib" --- SMTP 協定用戶端
*****************************

**原始碼：**Lib/smtplib.py

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

The "smtplib" module defines an SMTP client session object that can be
used to send mail to any internet machine with an SMTP or ESMTP
listener daemon.  For details of SMTP and ESMTP operation, consult
**RFC 821** (Simple Mail Transfer Protocol) and **RFC 1869** (SMTP
Service Extensions).

適用：非 WASI。

此模組在 WebAssembly 平台上不起作用或無法使用。更多資訊請參閱
WebAssembly 平台。

class smtplib.SMTP(host='', port=0, local_hostname=None, [timeout, ]source_address=None)

   An "SMTP" instance encapsulates an SMTP connection.  It has methods
   that support a full repertoire of SMTP and ESMTP operations. If the
   optional *host* and *port* parameters are given, the SMTP
   "connect()" method is called with those parameters during
   initialization.  If specified, *local_hostname* is used as the FQDN
   of the local host in the HELO/EHLO command.  Otherwise, the local
   hostname is found using "socket.getfqdn()".  If the "connect()"
   call returns anything other than a success code, an
   "SMTPConnectError" is raised. The optional *timeout* parameter
   specifies a timeout in seconds for blocking operations like the
   connection attempt (if not specified, the global default timeout
   setting will be used).  If the timeout expires, "TimeoutError" is
   raised.  The optional *source_address* parameter allows binding to
   some specific source address in a machine with multiple network
   interfaces, and/or to some specific source TCP port. It takes a
   2-tuple "(host, port)", for the socket to bind to as its source
   address before connecting. If omitted (or if *host* or *port* are
   "''" and/or "0" respectively) the OS default behavior will be used.

   For normal use, you should only require the initialization/connect,
   "sendmail()", and "SMTP.quit()" methods. An example is included
   below.

   The "SMTP" class supports the "with" statement.  When used like
   this, the SMTP "QUIT" command is issued automatically when the
   "with" statement exits.  E.g.:

      >>> from smtplib import SMTP
      >>> with SMTP("domain.org") as smtp:
      ...     smtp.noop()
      ...
      (250, b'Ok')
      >>>

   所有指令都會引發一個附帶引數 "self"、"data" 的稽核事件
   "smtplib.SMTP.send"，其中 "data" 為即將傳送至遠端的位元組。

   在 3.3 版的變更: Support for the "with" statement was added.

   在 3.3 版的變更: 新增 source_address 引數。

   在 3.5 版被加入: The SMTPUTF8 extension (**RFC 6531**) is now
   supported.

   在 3.9 版的變更: If the *timeout* parameter is set to be zero, it
   will raise a "ValueError" to prevent the creation of a non-blocking
   socket.

class smtplib.SMTP_SSL(host='', port=0, local_hostname=None, *, [timeout, ]context=None, source_address=None)

   An "SMTP_SSL" instance behaves exactly the same as instances of
   "SMTP". "SMTP_SSL" should be used for situations where SSL is
   required from the beginning of the connection and using
   "starttls()" is not appropriate. If *host* is not specified, the
   local host is used. If *port* is zero, the standard SMTP-over-SSL
   port (465) is used.  The optional arguments *local_hostname*,
   *timeout* and *source_address* have the same meaning as they do in
   the "SMTP" class.  *context*, also optional, can contain a
   "SSLContext" and allows configuring various aspects of the secure
   connection.  Please read Security considerations for best
   practices.

   在 3.3 版的變更: 新增 *context*。

   在 3.3 版的變更: 新增 *source_address* 引數。

   在 3.4 版的變更: The class now supports hostname check with
   "ssl.SSLContext.check_hostname" and *Server Name Indication* (see
   "ssl.HAS_SNI").

   在 3.9 版的變更: If the *timeout* parameter is set to be zero, it
   will raise a "ValueError" to prevent the creation of a non-blocking
   socket

   在 3.12 版的變更: The deprecated *keyfile* and *certfile*
   parameters have been removed.

class smtplib.LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None[, timeout])

   The LMTP protocol, which is very similar to ESMTP, is heavily based
   on the standard SMTP client. It's common to use Unix sockets for
   LMTP, so our "connect()" method must support that as well as a
   regular host:port server. The optional arguments *local_hostname*
   and *source_address* have the same meaning as they do in the "SMTP"
   class. To specify a Unix socket, you must use an absolute path for
   *host*, starting with a '/'.

   Authentication is supported, using the regular SMTP mechanism. When
   using a Unix socket, LMTP generally don't support or require any
   authentication, but your mileage might vary.

   在 3.9 版的變更: 新增 *timeout* 選用參數。

A nice selection of exceptions is defined as well:

exception smtplib.SMTPException

   Subclass of "OSError" that is the base exception class for all the
   other exceptions provided by this module.

   在 3.4 版的變更: SMTPException became subclass of "OSError"

exception smtplib.SMTPServerDisconnected

   This exception is raised when the server unexpectedly disconnects,
   or when an attempt is made to use the "SMTP" instance before
   connecting it to a server.

exception smtplib.SMTPResponseException

   Base class for all exceptions that include an SMTP error code.
   These exceptions are generated in some instances when the SMTP
   server returns an error code.  The error code is stored in the
   "smtp_code" attribute of the error, and the "smtp_error" attribute
   is set to the error message.

exception smtplib.SMTPSenderRefused

   Sender address refused.  In addition to the attributes set by on
   all "SMTPResponseException" exceptions, this sets 'sender' to the
   string that the SMTP server refused.

exception smtplib.SMTPRecipientsRefused

   All recipient addresses refused.  The errors for each recipient are
   accessible through the attribute "recipients", which is a
   dictionary of exactly the same sort as "SMTP.sendmail()" returns.

exception smtplib.SMTPDataError

   The SMTP server refused to accept the message data.

exception smtplib.SMTPConnectError

   Error occurred during establishment of a connection  with the
   server.

exception smtplib.SMTPHeloError

   The server refused our "HELO" message.

exception smtplib.SMTPNotSupportedError

   The command or option attempted is not supported by the server.

   在 3.5 版被加入.

exception smtplib.SMTPAuthenticationError

   SMTP authentication went wrong.  Most probably the server didn't
   accept the username/password combination provided.

也參考:

  **RFC 821** - Simple Mail Transfer Protocol
     Protocol definition for SMTP.  This document covers the model,
     operating procedure, and protocol details for SMTP.

  **RFC 1869** - SMTP Service Extensions
     Definition of the ESMTP extensions for SMTP.  This describes a
     framework for extending SMTP with new commands, supporting
     dynamic discovery of the commands provided by the server, and
     defines a few additional commands.


SMTP 物件
=========

An "SMTP" instance has the following methods:

SMTP.set_debuglevel(level)

   Set the debug output level.  A value of 1 or "True" for *level*
   results in debug messages for connection and for all messages sent
   to and received from the server.  A value of 2 for *level* results
   in these messages being timestamped.

   在 3.5 版的變更: Added debuglevel 2.

SMTP.docmd(cmd, args='')

   Send a command *cmd* to the server.  The optional argument *args*
   is simply concatenated to the command, separated by a space.

   This returns a 2-tuple composed of a numeric response code and the
   actual response line (multiline responses are joined into one long
   line.)

   In normal operation it should not be necessary to call this method
   explicitly. It is used to implement other methods and may be useful
   for testing private extensions.

   If the connection to the server is lost while waiting for the
   reply, "SMTPServerDisconnected" will be raised.

SMTP.connect(host='localhost', port=0)

   Connect to a host on a given port.  The defaults are to connect to
   the local host at the standard SMTP port (25). If the hostname ends
   with a colon ("':'") followed by a number, that suffix will be
   stripped off and the number interpreted as the port number to use.
   This method is automatically invoked by the constructor if a host
   is specified during instantiation.  Returns a 2-tuple of the
   response code and message sent by the server in its connection
   response.

   引發一個附帶引數 "self"、"host"、"port" 的稽核事件
   "smtplib.connect"。

SMTP.helo(name='')

   Identify yourself to the SMTP server using "HELO".  The hostname
   argument defaults to the fully qualified domain name of the local
   host. The message returned by the server is stored as the
   "helo_resp" attribute of the object.

   In normal operation it should not be necessary to call this method
   explicitly. It will be implicitly called by the "sendmail()" when
   necessary.

SMTP.ehlo(name='')

   Identify yourself to an ESMTP server using "EHLO".  The hostname
   argument defaults to the fully qualified domain name of the local
   host.  Examine the response for ESMTP option and store them for use
   by "has_extn()". Also sets several informational attributes: the
   message returned by the server is stored as the "ehlo_resp"
   attribute, "does_esmtp" is set to "True" or "False" depending on
   whether the server supports ESMTP, and "esmtp_features" will be a
   dictionary containing the names of the SMTP service extensions this
   server supports, and their parameters (if any).

   Unless you wish to use "has_extn()" before sending mail, it should
   not be necessary to call this method explicitly.  It will be
   implicitly called by "sendmail()" when necessary.

SMTP.ehlo_or_helo_if_needed()

   This method calls "ehlo()" and/or "helo()" if there has been no
   previous "EHLO" or "HELO" command this session.  It tries ESMTP
   "EHLO" first.

   "SMTPHeloError"
      The server didn't reply properly to the "HELO" greeting.

SMTP.has_extn(name)

   Return "True" if *name* is in the set of SMTP service extensions
   returned by the server, "False" otherwise. Case is ignored.

SMTP.verify(address)

   Check the validity of an address on this server using SMTP "VRFY".
   Returns a tuple consisting of code 250 and a full **RFC 822**
   address (including human name) if the user address is valid.
   Otherwise returns an SMTP error code of 400 or greater and an error
   string.

   備註:

     Many sites disable SMTP "VRFY" in order to foil spammers.

SMTP.login(user, password, *, initial_response_ok=True)

   Log in on an SMTP server that requires authentication. The
   arguments are the username and the password to authenticate with.
   If there has been no previous "EHLO" or "HELO" command this
   session, this method tries ESMTP "EHLO" first. This method will
   return normally if the authentication was successful, or may raise
   the following exceptions:

   "SMTPHeloError"
      The server didn't reply properly to the "HELO" greeting.

   "SMTPAuthenticationError"
      The server didn't accept the username/password combination.

   "SMTPNotSupportedError"
      The "AUTH" command is not supported by the server.

   "SMTPException"
      No suitable authentication method was found.

   Each of the authentication methods supported by "smtplib" are tried
   in turn if they are advertised as supported by the server.  See
   "auth()" for a list of supported authentication methods.
   *initial_response_ok* is passed through to "auth()".

   Optional keyword argument *initial_response_ok* specifies whether,
   for authentication methods that support it, an "initial response"
   as specified in **RFC 4954** can be sent along with the "AUTH"
   command, rather than requiring a challenge/response.

   在 3.5 版的變更: "SMTPNotSupportedError" may be raised, and the
   *initial_response_ok* parameter was added.

SMTP.auth(mechanism, authobject, *, initial_response_ok=True)

   Issue an "SMTP" "AUTH" command for the specified authentication
   *mechanism*, and handle the challenge response via *authobject*.

   *mechanism* specifies which authentication mechanism is to be used
   as argument to the "AUTH" command; the valid values are those
   listed in the "auth" element of "esmtp_features".

   *authobject* must be a callable object taking an optional single
   argument:

      data = authobject(challenge=None)

   If optional keyword argument *initial_response_ok* is true,
   "authobject()" will be called first with no argument.  It can
   return the **RFC 4954** "initial response" ASCII "str" which will
   be encoded and sent with the "AUTH" command as below.  If the
   "authobject()" does not support an initial response (e.g. because
   it requires a challenge), it should return "None" when called with
   "challenge=None".  If *initial_response_ok* is false, then
   "authobject()" will not be called first with "None".

   If the initial response check returns "None", or if
   *initial_response_ok* is false, "authobject()" will be called to
   process the server's challenge response; the *challenge* argument
   it is passed will be a "bytes".  It should return ASCII "str"
   *data* that will be base64 encoded and sent to the server.

   The "SMTP" class provides "authobjects" for the "CRAM-MD5",
   "PLAIN", and "LOGIN" mechanisms; they are named
   "SMTP.auth_cram_md5", "SMTP.auth_plain", and "SMTP.auth_login"
   respectively.  They all require that the "user" and "password"
   properties of the "SMTP" instance are set to appropriate values.

   User code does not normally need to call "auth" directly, but can
   instead call the "login()" method, which will try each of the above
   mechanisms in turn, in the order listed.  "auth" is exposed to
   facilitate the implementation of authentication methods not (or not
   yet) supported directly by "smtplib".

   在 3.5 版被加入.

SMTP.starttls(*, context=None)

   Put the SMTP connection in TLS (Transport Layer Security) mode.
   All SMTP commands that follow will be encrypted.  You should then
   call "ehlo()" again.

   If *keyfile* and *certfile* are provided, they are used to create
   an "ssl.SSLContext".

   Optional *context* parameter is an "ssl.SSLContext" object; This is
   an alternative to using a keyfile and a certfile and if specified
   both *keyfile* and *certfile* should be "None".

   If there has been no previous "EHLO" or "HELO" command this
   session, this method tries ESMTP "EHLO" first.

   在 3.12 版的變更: The deprecated *keyfile* and *certfile*
   parameters have been removed.

   "SMTPHeloError"
      The server didn't reply properly to the "HELO" greeting.

   "SMTPNotSupportedError"
      The server does not support the STARTTLS extension.

   "RuntimeError"
      SSL/TLS support is not available to your Python interpreter.

   在 3.3 版的變更: 新增 *context*。

   在 3.4 版的變更: The method now supports hostname check with
   "SSLContext.check_hostname" and *Server Name Indicator* (see
   "HAS_SNI").

   在 3.5 版的變更: The error raised for lack of STARTTLS support is
   now the "SMTPNotSupportedError" subclass instead of the base
   "SMTPException".

SMTP.sendmail(from_addr, to_addrs, msg, mail_options=(), rcpt_options=())

   Send mail.  The required arguments are an **RFC 822** from-address
   string, a list of **RFC 822** to-address strings (a bare string
   will be treated as a list with 1 address), and a message string.
   The caller may pass a list of ESMTP options (such as "8bitmime") to
   be used in "MAIL FROM" commands as *mail_options*. ESMTP options
   (such as "DSN" commands) that should be used with all "RCPT"
   commands can be passed as *rcpt_options*.  (If you need to use
   different ESMTP options to different recipients you have to use the
   low-level methods such as "mail()", "rcpt()" and "data()" to send
   the message.)

   備註:

     The *from_addr* and *to_addrs* parameters are used to construct
     the message envelope used by the transport agents.  "sendmail"
     does not modify the message headers in any way.

   *msg* may be a string containing characters in the ASCII range, or
   a byte string.  A string is encoded to bytes using the ascii codec,
   and lone "\r" and "\n" characters are converted to "\r\n"
   characters.  A byte string is not modified.

   If there has been no previous "EHLO" or "HELO" command this
   session, this method tries ESMTP "EHLO" first. If the server does
   ESMTP, message size and each of the specified options will be
   passed to it (if the option is in the feature set the server
   advertises).  If "EHLO" fails, "HELO" will be tried and ESMTP
   options suppressed.

   This method will return normally if the mail is accepted for at
   least one recipient. Otherwise it will raise an exception.  That
   is, if this method does not raise an exception, then someone should
   get your mail. If this method does not raise an exception, it
   returns a dictionary, with one entry for each recipient that was
   refused.  Each entry contains a tuple of the SMTP error code and
   the accompanying error message sent by the server.

   If "SMTPUTF8" is included in *mail_options*, and the server
   supports it, *from_addr* and *to_addrs* may contain non-ASCII
   characters.

   This method may raise the following exceptions:

   "SMTPRecipientsRefused"
      All recipients were refused.  Nobody got the mail.  The
      "recipients" attribute of the exception object is a dictionary
      with information about the refused recipients (like the one
      returned when at least one recipient was accepted).

   "SMTPHeloError"
      The server didn't reply properly to the "HELO" greeting.

   "SMTPSenderRefused"
      The server didn't accept the *from_addr*.

   "SMTPDataError"
      The server replied with an unexpected error code (other than a
      refusal of a recipient).

   "SMTPNotSupportedError"
      "SMTPUTF8" was given in the *mail_options* but is not supported
      by the server.

   Unless otherwise noted, the connection will be open even after an
   exception is raised.

   在 3.2 版的變更: *msg* may be a byte string.

   在 3.5 版的變更: "SMTPUTF8" support added, and
   "SMTPNotSupportedError" may be raised if "SMTPUTF8" is specified
   but the server does not support it.

SMTP.send_message(msg, from_addr=None, to_addrs=None, mail_options=(), rcpt_options=())

   This is a convenience method for calling "sendmail()" with the
   message represented by an "email.message.Message" object.  The
   arguments have the same meaning as for "sendmail()", except that
   *msg* is a "Message" object.

   If *from_addr* is "None" or *to_addrs* is "None", "send_message"
   fills those arguments with addresses extracted from the headers of
   *msg* as specified in **RFC 5322**: *from_addr* is set to the
   *Sender* field if it is present, and otherwise to the *From* field.
   *to_addrs* combines the values (if any) of the *To*, *Cc*, and
   *Bcc* fields from *msg*.  If exactly one set of *Resent-** headers
   appear in the message, the regular headers are ignored and the
   *Resent-** headers are used instead. If the message contains more
   than one set of *Resent-** headers, a "ValueError" is raised, since
   there is no way to unambiguously detect the most recent set of
   *Resent-* headers.

   "send_message" serializes *msg* using "BytesGenerator" with "\r\n"
   as the *linesep*, and calls "sendmail()" to transmit the resulting
   message.  Regardless of the values of *from_addr* and *to_addrs*,
   "send_message" does not transmit any *Bcc* or *Resent-Bcc* headers
   that may appear in *msg*.  If any of the addresses in *from_addr*
   and *to_addrs* contain non-ASCII characters and the server does not
   advertise "SMTPUTF8" support, an "SMTPNotSupported" error is
   raised.  Otherwise the "Message" is serialized with a clone of its
   "policy" with the "utf8" attribute set to "True", and "SMTPUTF8"
   and "BODY=8BITMIME" are added to *mail_options*.

   在 3.2 版被加入.

   在 3.5 版被加入: Support for internationalized addresses
   ("SMTPUTF8").

SMTP.quit()

   Terminate the SMTP session and close the connection.  Return the
   result of the SMTP "QUIT" command.

Low-level methods corresponding to the standard SMTP/ESMTP commands
"HELP", "RSET", "NOOP", "MAIL", "RCPT", and "DATA" are also supported.
Normally these do not need to be called directly, so they are not
documented here.  For details, consult the module code.


SMTP 範例
=========

This example prompts the user for addresses needed in the message
envelope ('To' and 'From' addresses), and the message to be delivered.
Note that the headers to be included with the message must be included
in the message as entered; this example doesn't do any processing of
the **RFC 822** headers.  In particular, the 'To' and 'From' addresses
must be included in the message headers explicitly:

   import smtplib

   def prompt(title):
       return input(title).strip()

   from_addr = prompt("From: ")
   to_addrs  = prompt("To: ").split()
   print("Enter message, end with ^D (Unix) or ^Z (Windows):")

   # Add the From: and To: headers at the start!
   lines = [f"From: {from_addr}", f"To: {', '.join(to_addrs)}", ""]
   while True:
       try:
           line = input()
       except EOFError:
           break
       else:
           lines.append(line)

   msg = "\r\n".join(lines)
   print("Message length is", len(msg))

   server = smtplib.SMTP("localhost")
   server.set_debuglevel(1)
   server.sendmail(from_addr, to_addrs, msg)
   server.quit()

備註:

  In general, you will want to use the "email" package's features to
  construct an email message, which you can then send via
  "send_message()"; see email：範例.
