# 21.17. `smtplib` — SMTP protocol client

Source code: 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).

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, `socket.timeout` is raised. The optional source_address parameter allows to bind 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 `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')
      >>>

  Changed in version 3.3: Support for the `with` statement was added.

  Changed in version 3.3: source_address argument was added.

class `smtplib.``SMTP_SSL`(host='', port=0, local_hostname=None, keyfile=None, certfile=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 to configure various aspects of the secure connection. Please read Security considerations for best practices.

  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.

  Changed in version 3.3: context was added.

  Changed in version 3.3: source_address argument was added.

  Changed in version 3.4: The class now supports hostname check with `ssl.SSLContext.check_hostname` and Server Name Indication (see `ssl.HAS_SNI`).

class `smtplib.``LMTP`(host='', port=LMTP_PORT, local_hostname=None, source_address=None)

  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.

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.

  Changed in version 3.4: 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.``SMTPAuthenticationError`

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

See also

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.

## 21.17.1. SMTP Objects

An `SMTP` instance has the following methods:

`SMTP.``set_debuglevel`(level)

  Set the debug output level. A true value for level results in debug messages for connection and for all messages sent to and received from the server.

`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.

`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 call `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.

  Note

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

`SMTP.``login`(user, password)

  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.
  `SMTPException`
    No suitable authentication method was found.

`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, these are passed to the `socket` module’s `ssl()` function.

  Optional context parameter is a `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.

  `SMTPHeloError`
    The server didn’t reply properly to the `HELO` greeting.
  `SMTPException`
    The server does not support the STARTTLS extension.
  `RuntimeError`
    SSL/TLS support is not available to your Python interpreter.

  Changed in version 3.3: context was added.

  Changed in version 3.4: The method now supports hostname check with `SSLContext.check_hostname` and Server Name Indicator (see `HAS_SNI`).

`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.)

  Note

  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.

  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).

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

  Changed in version 3.2: msg may be a byte string.

`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 2822: from_addr is set to the Sender field if it is present, and otherwise to the From field. to_adresses 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.

  New in version 3.2.

`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.

## 21.17.2. 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:
        try:
            line = input()
        except EOFError:
            break
        if not line:
            break
        msg = msg + line

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

    server = smtplib.SMTP('localhost')
    server.set_debuglevel(1)
    server.sendmail(fromaddr, toaddrs, msg)
    server.quit()

Note

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: Examples.