smtplib ---SMTP协议客户端

源代码: Lib/

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).

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.

正常使用时,只需要初始化或 connect 方法,sendmail() 方法,再加上 SMTP.quit() 方法即可。下文包括了一个示例。

SMTP 类支持 with 语句。当这样使用时,with 语句一退出就会自动发出 SMTP QUIT 命令。例如:

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

All commands will raise an auditing event smtplib.SMTP.send with arguments self and data, where data is the bytes about to be sent to the remote host.

3.3 版更變: 添加了对 with 语句的支持。

3.3 版更變: source_address argument was added.

3.5 版新加入: The SMTPUTF8 extension (RFC 6531) is now supported.

3.9 版更變: 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, keyfile=None, certfile=None, [timeout, ]context=None, source_address=None)

SMTP_SSL 实例与 SMTP 实例的行为完全相同。在开始连接就需要 SSL,且 starttls() 不适合的情况下,应该使用 SMTP_SSL。如果未指定 host,则使用 localhost。如果 port 为 0,则使用标准 SMTP-over-SSL 端口(465)。可选参数 local_hostnametimeoutsource_address 的含义与 SMTP 类中的相同。可选参数 context 是一个 SSLContext 对象,可以从多个方面配置安全连接。请阅读 安全考量 以获取最佳实践。

keyfile and certfile are a legacy alternative to context, and can point to a PEM formatted private key and certificate chain file for the SSL connection.

3.3 版更變: 增加了 context

3.3 版更變: source_address argument was added.

3.4 版更變: 本类现在支持使用 ssl.SSLContext.check_hostname服务器名称指示 (参阅 ssl.HAS_SNI)进行主机名检查。

3.6 版後已棄用: keyfilecertfile 已弃用并转而推荐 context。 请改用 ssl.SSLContext.load_cert_chain() 或让 ssl.create_default_context() 为你选择系统所信任的 CA 证书。

3.9 版更變: 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.LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None[, timeout])

LMTP 协议与 ESMTP 非常相似,它很大程度上基于标准的 SMTP 客户端。将 Unix 套接字用于 LMTP 是很常见的,因此 connect() 方法支持 Unix 套接字,也支持常规的 host:port 服务器。可选参数 local_hostname 和 source_address 的含义与 SMTP 类中的相同。要指定 Unix 套接字,host 必须使用绝对路径,以 '/' 开头。

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.

3.9 版更變: The optional timeout parameter was added.

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.

3.4 版更變: 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.

3.5 版新加入.

exception smtplib.SMTPAuthenticationError

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


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 Objects

An SMTP instance has the following methods:


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.

3.5 版更變: 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)

连接到某个主机的某个端口。默认是连接到 localhost 的标准 SMTP 端口(25)上。如果主机名以冒号 (':') 结尾,后跟数字,则该后缀将被删除,且数字将视作要使用的端口号。如果在实例化时指定了 host,则构造函数会自动调用本方法。返回包含响应码和响应消息的 2 元组,它们由服务器在其连接响应中发送。

Raises an auditing event smtplib.connect with arguments self, host, port.


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.


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.


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


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


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


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.


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:


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


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


The AUTH command is not supported by the server.


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.

3.5 版更變: 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.

3.5 版新加入.

SMTP.starttls(keyfile=None, certfile=None, 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.

3.6 版後已棄用: keyfilecertfile 已弃用并转而推荐 context。 请改用 ssl.SSLContext.load_cert_chain() 或让 ssl.create_default_context() 为你选择系统所信任的 CA 证书。


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


The server does not support the STARTTLS extension.


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

3.3 版更變: 增加了 context

3.4 版更變: The method now supports hostname check with SSLContext.check_hostname and Server Name Indicator (see HAS_SNI).

3.5 版更變: 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=())

发送邮件。必要参数是一个 RFC 822 发件地址字符串,一个 RFC 822 收件地址字符串列表(裸字符串将被视为含有 1 个地址的列表),以及一个消息字符串。调用者可以将 ESMTP 选项列表(如 8bitmime)作为 mail_options 传入,用于 MAIL FROM 命令。需要与所有 RCPT 命令一起使用的 ESMTP 选项(如 DSN 命令)可以作为 rcpt_options 传入。(如果需要对不同的收件人使用不同的 ESMTP 选项,则必须使用底层的方法来发送消息,如 mail(), rcpt()data()。)


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:


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).


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


The server didn't accept the from_addr.


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


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.

3.2 版更變: msg may be a byte string.

3.5 版更變: 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=())

本方法是一种快捷方法,用于带着消息调用 sendmail(),消息由 email.message.Message 对象表示。参数的含义与 sendmail() 中的相同,除了 msg,它是一个 Message 对象。

如果 from_addrNoneto_addrsNone,那么``send_message``将根据 RFC 5322,从 msg 头部提取地址填充下列参数:如果头部存在 Sender 字段,则用它填充 from_addr,不存在则用 From 字段填充 from_addrto_addrs 组合了 msg 中的 To, CcBcc 字段的值(字段存在的情况下)。如果一组 Resent-* 头部恰好出现在 message 中,那么就忽略常规的头部,改用 Resent-* 头部。如果 message 包含多组 Resent-* 头部,则引发 ValueError,因为无法明确检测出哪一组 Resent- 头部是最新的。

send_message 使用 BytesGenerator 来序列化 msg,且将 \r\n 作为 linesep,并调用 sendmail() 来传输序列化后的结果。无论 from_addrto_addrs 的值为何,send_message 都不会传输 msg 中可能出现的 BccResent-Bcc 头部。如果 from_addrto_addrs 中的某个地址包含非 ASCII 字符,且服务器没有声明支持 SMTPUTF8,则引发 SMTPNotSupported 错误。如果服务器支持,则 Message 将按新克隆的 policy 进行序列化,其中的 utf8 属性被设置为 True,且 SMTPUTF8BODY=8BITMIME 被添加到 mail_options 中。

3.2 版新加入.

3.5 版新加入: Support for internationalized addresses (SMTPUTF8).


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 Example

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

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

# Add the From: and To: headers at the start!
msg = ("From: %s\r\nTo: %s\r\n\r\n"
       % (fromaddr, ", ".join(toaddrs)))
while True:
        line = input()
    except EOFError:
    if not line:
    msg = msg + line

print("Message length is", len(msg))

server = smtplib.SMTP('localhost')
server.sendmail(fromaddr, toaddrs, msg)


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: 示例.