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[gae.git] / python / lib / django_1_4 / docs / topics / email.txt

=============
Sending email
=============

.. module:: django.core.mail
   :synopsis: Helpers to easily send email.

Although Python makes sending email relatively easy via the :mod:`smtplib`
module, Django provides a couple of light wrappers over it. These wrappers are
provided to make sending email extra quick, to make it easy to test email
sending during development, and to provide support for platforms that can't use
SMTP.

The code lives in the ``django.core.mail`` module.

Quick example
=============

In two lines::

    from django.core.mail import send_mail

    send_mail('Subject here', 'Here is the message.', 'from@example.com',
        ['to@example.com'], fail_silently=False)

Mail is sent using the SMTP host and port specified in the
:setting:`EMAIL_HOST` and :setting:`EMAIL_PORT` settings. The
:setting:`EMAIL_HOST_USER` and :setting:`EMAIL_HOST_PASSWORD` settings, if
set, are used to authenticate to the SMTP server, and the
:setting:`EMAIL_USE_TLS` setting controls whether a secure connection is used.

.. note::

    The character set of email sent with ``django.core.mail`` will be set to
    the value of your :setting:`DEFAULT_CHARSET` setting.

send_mail()
===========

.. function:: send_mail(subject, message, from_email, recipient_list, fail_silently=False, auth_user=None, auth_password=None, connection=None)

The simplest way to send email is using
``django.core.mail.send_mail()``.

The ``subject``, ``message``, ``from_email`` and ``recipient_list`` parameters
are required.

* ``subject``: A string.
* ``message``: A string.
* ``from_email``: A string.
* ``recipient_list``: A list of strings, each an email address. Each
  member of ``recipient_list`` will see the other recipients in the "To:"
  field of the email message.
* ``fail_silently``: A boolean. If it's ``False``, ``send_mail`` will raise
  an :exc:`smtplib.SMTPException`. See the :mod:`smtplib` docs for a list of
  possible exceptions, all of which are subclasses of
  :exc:`~smtplib.SMTPException`.
* ``auth_user``: The optional username to use to authenticate to the SMTP
  server. If this isn't provided, Django will use the value of the
  :setting:`EMAIL_HOST_USER` setting.
* ``auth_password``: The optional password to use to authenticate to the
  SMTP server. If this isn't provided, Django will use the value of the
  :setting:`EMAIL_HOST_PASSWORD` setting.
* ``connection``: The optional email backend to use to send the mail.
  If unspecified, an instance of the default backend will be used.
  See the documentation on :ref:`Email backends <topic-email-backends>`
  for more details.

send_mass_mail()
================

.. function:: send_mass_mail(datatuple, fail_silently=False, auth_user=None, auth_password=None, connection=None)

``django.core.mail.send_mass_mail()`` is intended to handle mass emailing.

``datatuple`` is a tuple in which each element is in this format::

    (subject, message, from_email, recipient_list)

``fail_silently``, ``auth_user`` and ``auth_password`` have the same functions
as in :meth:`~django.core.mail.send_mail()`.

Each separate element of ``datatuple`` results in a separate email message.
As in :meth:`~django.core.mail.send_mail()`, recipients in the same
``recipient_list`` will all see the other addresses in the email messages'
"To:" field.

For example, the following code would send two different messages to
two different sets of recipients; however, only one connection to the
mail server would be opened::

    message1 = ('Subject here', 'Here is the message', 'from@example.com', ['first@example.com', 'other@example.com'])
    message2 = ('Another Subject', 'Here is another message', 'from@example.com', ['second@test.com'])
    send_mass_mail((message1, message2), fail_silently=False)

send_mass_mail() vs. send_mail()
--------------------------------

The main difference between :meth:`~django.core.mail.send_mass_mail()` and
:meth:`~django.core.mail.send_mail()` is that
:meth:`~django.core.mail.send_mail()` opens a connection to the mail server
each time it's executed, while :meth:`~django.core.mail.send_mass_mail()` uses
a single connection for all of its messages. This makes
:meth:`~django.core.mail.send_mass_mail()` slightly more efficient.

mail_admins()
=============

.. function:: mail_admins(subject, message, fail_silently=False, connection=None, html_message=None)

``django.core.mail.mail_admins()`` is a shortcut for sending an email to the
site admins, as defined in the :setting:`ADMINS` setting.

``mail_admins()`` prefixes the subject with the value of the
:setting:`EMAIL_SUBJECT_PREFIX` setting, which is ``"[Django] "`` by default.

The "From:" header of the email will be the value of the
:setting:`SERVER_EMAIL` setting.

This method exists for convenience and readability.

.. versionchanged:: 1.3

If ``html_message`` is provided, the resulting email will be a
:mimetype:`multipart/alternative` email with ``message`` as the
:mimetype:`text/plain` content type and ``html_message`` as the
:mimetype:`text/html` content type.

mail_managers()
===============

.. function:: mail_managers(subject, message, fail_silently=False, connection=None, html_message=None)

``django.core.mail.mail_managers()`` is just like ``mail_admins()``, except it
sends an email to the site managers, as defined in the :setting:`MANAGERS`
setting.

Examples
========

This sends a single email to john@example.com and jane@example.com, with them
both appearing in the "To:"::

    send_mail('Subject', 'Message.', 'from@example.com',
        ['john@example.com', 'jane@example.com'])

This sends a message to john@example.com and jane@example.com, with them both
receiving a separate email::

    datatuple = (
        ('Subject', 'Message.', 'from@example.com', ['john@example.com']),
        ('Subject', 'Message.', 'from@example.com', ['jane@example.com']),
    )
    send_mass_mail(datatuple)

Preventing header injection
===========================

`Header injection`_ is a security exploit in which an attacker inserts extra
email headers to control the "To:" and "From:" in email messages that your
scripts generate.

The Django email functions outlined above all protect against header injection
by forbidding newlines in header values. If any ``subject``, ``from_email`` or
``recipient_list`` contains a newline (in either Unix, Windows or Mac style),
the email function (e.g. :meth:`~django.core.mail.send_mail()`) will raise
``django.core.mail.BadHeaderError`` (a subclass of ``ValueError``) and, hence,
will not send the email. It's your responsibility to validate all data before
passing it to the email functions.

If a ``message`` contains headers at the start of the string, the headers will
simply be printed as the first bit of the email message.

Here's an example view that takes a ``subject``, ``message`` and ``from_email``
from the request's POST data, sends that to admin@example.com and redirects to
"/contact/thanks/" when it's done::

    from django.core.mail import send_mail, BadHeaderError

    def send_email(request):
        subject = request.POST.get('subject', '')
        message = request.POST.get('message', '')
        from_email = request.POST.get('from_email', '')
        if subject and message and from_email:
            try:
                send_mail(subject, message, from_email, ['admin@example.com'])
            except BadHeaderError:
                return HttpResponse('Invalid header found.')
            return HttpResponseRedirect('/contact/thanks/')
        else:
            # In reality we'd use a form class
            # to get proper validation errors.
            return HttpResponse('Make sure all fields are entered and valid.')

.. _Header injection: http://www.nyphp.org/phundamentals/8_Preventing-Email-Header-Injection

.. _emailmessage-and-smtpconnection:

The EmailMessage class
======================

Django's :meth:`~django.core.mail.send_mail()` and
:meth:`~django.core.mail.send_mass_mail()` functions are actually thin
wrappers that make use of the :class:`~django.core.mail.EmailMessage` class.

Not all features of the :class:`~django.core.mail.EmailMessage` class are
available through the :meth:`~django.core.mail.send_mail()` and related
wrapper functions. If you wish to use advanced features, such as BCC'ed
recipients, file attachments, or multi-part email, you'll need to create
:class:`~django.core.mail.EmailMessage` instances directly.

.. note::
    This is a design feature. :meth:`~django.core.mail.send_mail()` and
    related functions were originally the only interface Django provided.
    However, the list of parameters they accepted was slowly growing over
    time. It made sense to move to a more object-oriented design for email
    messages and retain the original functions only for backwards
    compatibility.

:class:`~django.core.mail.EmailMessage` is responsible for creating the email
message itself. The :ref:`email backend <topic-email-backends>` is then
responsible for sending the email.

For convenience, :class:`~django.core.mail.EmailMessage` provides a simple
``send()`` method for sending a single email. If you need to send multiple
messages, the email backend API :ref:`provides an alternative
<topics-sending-multiple-emails>`.

EmailMessage Objects
--------------------

.. class:: EmailMessage

The :class:`~django.core.mail.EmailMessage` class is initialized with the
following parameters (in the given order, if positional arguments are used).
All parameters are optional and can be set at any time prior to calling the
``send()`` method.

.. versionchanged:: 1.3
   The ``cc`` argument was added.

* ``subject``: The subject line of the email.

* ``body``: The body text. This should be a plain text message.

* ``from_email``: The sender's address. Both ``fred@example.com`` and
  ``Fred <fred@example.com>`` forms are legal. If omitted, the
  :setting:`DEFAULT_FROM_EMAIL` setting is used.

* ``to``: A list or tuple of recipient addresses.

* ``bcc``: A list or tuple of addresses used in the "Bcc" header when
  sending the email.

* ``connection``: An email backend instance. Use this parameter if
  you want to use the same connection for multiple messages. If omitted, a
  new connection is created when ``send()`` is called.

* ``attachments``: A list of attachments to put on the message. These can
  be either ``email.MIMEBase.MIMEBase`` instances, or ``(filename,
  content, mimetype)`` triples.

* ``headers``: A dictionary of extra headers to put on the message. The
  keys are the header name, values are the header values. It's up to the
  caller to ensure header names and values are in the correct format for
  an email message.

* ``cc``: A list or tuple of recipient addresses used in the "Cc" header
  when sending the email.

For example::

    email = EmailMessage('Hello', 'Body goes here', 'from@example.com',
                ['to1@example.com', 'to2@example.com'], ['bcc@example.com'],
                headers = {'Reply-To': 'another@example.com'})

The class has the following methods:

* ``send(fail_silently=False)`` sends the message. If a connection was
  specified when the email was constructed, that connection will be used.
  Otherwise, an instance of the default backend will be instantiated and
  used. If the keyword argument ``fail_silently`` is ``True``, exceptions
  raised while sending the message will be quashed.

* ``message()`` constructs a ``django.core.mail.SafeMIMEText`` object (a
  subclass of Python's ``email.MIMEText.MIMEText`` class) or a
  ``django.core.mail.SafeMIMEMultipart`` object holding the message to be
  sent. If you ever need to extend the
  :class:`~django.core.mail.EmailMessage` class, you'll probably want to
  override this method to put the content you want into the MIME object.

* ``recipients()`` returns a list of all the recipients of the message,
  whether they're recorded in the ``to``, ``cc`` or ``bcc`` attributes. This
  is another method you might need to override when subclassing, because the
  SMTP server needs to be told the full list of recipients when the message
  is sent. If you add another way to specify recipients in your class, they
  need to be returned from this method as well.

* ``attach()`` creates a new file attachment and adds it to the message.
  There are two ways to call ``attach()``:

  * You can pass it a single argument that is an
    ``email.MIMEBase.MIMEBase`` instance. This will be inserted directly
    into the resulting message.

  * Alternatively, you can pass ``attach()`` three arguments:
    ``filename``, ``content`` and ``mimetype``. ``filename`` is the name
    of the file attachment as it will appear in the email, ``content`` is
    the data that will be contained inside the attachment and
    ``mimetype`` is the optional MIME type for the attachment. If you
    omit ``mimetype``, the MIME content type will be guessed from the
    filename of the attachment.

    For example::

       message.attach('design.png', img_data, 'image/png')

* ``attach_file()`` creates a new attachment using a file from your
  filesystem. Call it with the path of the file to attach and, optionally,
  the MIME type to use for the attachment. If the MIME type is omitted, it
  will be guessed from the filename. The simplest use would be::

    message.attach_file('/images/weather_map.png')

.. _DEFAULT_FROM_EMAIL: ../settings/#default-from-email

Sending alternative content types
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It can be useful to include multiple versions of the content in an email; the
classic example is to send both text and HTML versions of a message. With
Django's email library, you can do this using the ``EmailMultiAlternatives``
class. This subclass of :class:`~django.core.mail.EmailMessage` has an
``attach_alternative()`` method for including extra versions of the message
body in the email. All the other methods (including the class initialization)
are inherited directly from :class:`~django.core.mail.EmailMessage`.

To send a text and HTML combination, you could write::

    from django.core.mail import EmailMultiAlternatives

    subject, from_email, to = 'hello', 'from@example.com', 'to@example.com'
    text_content = 'This is an important message.'
    html_content = '<p>This is an <strong>important</strong> message.</p>'
    msg = EmailMultiAlternatives(subject, text_content, from_email, [to])
    msg.attach_alternative(html_content, "text/html")
    msg.send()

By default, the MIME type of the ``body`` parameter in an
:class:`~django.core.mail.EmailMessage` is ``"text/plain"``. It is good
practice to leave this alone, because it guarantees that any recipient will be
able to read the email, regardless of their mail client. However, if you are
confident that your recipients can handle an alternative content type, you can
use the ``content_subtype`` attribute on the
:class:`~django.core.mail.EmailMessage` class to change the main content type.
The major type will always be ``"text"``, but you can change the
subtype. For example::

    msg = EmailMessage(subject, html_content, from_email, [to])
    msg.content_subtype = "html"  # Main content is now text/html
    msg.send()

.. _topic-email-backends:

Email backends
==============

.. versionadded:: 1.2

The actual sending of an email is handled by the email backend.

The email backend class has the following methods:

* ``open()`` instantiates an long-lived email-sending connection.

* ``close()`` closes the current email-sending connection.

* ``send_messages(email_messages)`` sends a list of
  :class:`~django.core.mail.EmailMessage` objects. If the connection is
  not open, this call will implicitly open the connection, and close the
  connection afterwards. If the connection is already open, it will be
  left open after mail has been sent.

Obtaining an instance of an email backend
-----------------------------------------

The :meth:`get_connection` function in ``django.core.mail`` returns an
instance of the email backend that you can use.

.. currentmodule:: django.core.mail

.. function:: get_connection(backend=None, fail_silently=False, *args, **kwargs)

By default, a call to ``get_connection()`` will return an instance of the
email backend specified in :setting:`EMAIL_BACKEND`. If you specify the
``backend`` argument, an instance of that backend will be instantiated.

The ``fail_silently`` argument controls how the backend should handle errors.
If ``fail_silently`` is True, exceptions during the email sending process
will be silently ignored.

All other arguments are passed directly to the constructor of the
email backend.

Django ships with several email sending backends. With the exception of the
SMTP backend (which is the default), these backends are only useful during
testing and development. If you have special email sending requirements, you
can :ref:`write your own email backend <topic-custom-email-backend>`.

.. _topic-email-smtp-backend:

SMTP backend
~~~~~~~~~~~~

This is the default backend. Email will be sent through a SMTP server.
The server address and authentication credentials are set in the
:setting:`EMAIL_HOST`, :setting:`EMAIL_PORT`, :setting:`EMAIL_HOST_USER`,
:setting:`EMAIL_HOST_PASSWORD` and :setting:`EMAIL_USE_TLS` settings in your
settings file.

The SMTP backend is the default configuration inherited by Django. If you
want to specify it explicitly, put the following in your settings::

    EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'

.. _topic-email-console-backend:

Console backend
~~~~~~~~~~~~~~~

Instead of sending out real emails the console backend just writes the
emails that would be send to the standard output. By default, the console
backend writes to ``stdout``. You can use a different stream-like object by
providing the ``stream`` keyword argument when constructing the connection.

To specify this backend, put the following in your settings::

    EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend'

This backend is not intended for use in production -- it is provided as a
convenience that can be used during development.

.. _topic-email-file-backend:

File backend
~~~~~~~~~~~~

The file backend writes emails to a file. A new file is created for each new
session that is opened on this backend. The directory to which the files are
written is either taken from the :setting:`EMAIL_FILE_PATH` setting or from
the ``file_path`` keyword when creating a connection with
:meth:`~django.core.mail.get_connection`.

To specify this backend, put the following in your settings::

    EMAIL_BACKEND = 'django.core.mail.backends.filebased.EmailBackend'
    EMAIL_FILE_PATH = '/tmp/app-messages' # change this to a proper location

This backend is not intended for use in production -- it is provided as a
convenience that can be used during development.

.. _topic-email-memory-backend:

In-memory backend
~~~~~~~~~~~~~~~~~

The ``'locmem'`` backend stores messages in a special attribute of the
``django.core.mail`` module. The ``outbox`` attribute is created when the
first message is sent. It's a list with an
:class:`~django.core.mail.EmailMessage` instance for each message that would
be send.

To specify this backend, put the following in your settings::

  EMAIL_BACKEND = 'django.core.mail.backends.locmem.EmailBackend'

This backend is not intended for use in production -- it is provided as a
convenience that can be used during development and testing.

.. _topic-email-dummy-backend:

Dummy backend
~~~~~~~~~~~~~

As the name suggests the dummy backend does nothing with your messages. To
specify this backend, put the following in your settings::

   EMAIL_BACKEND = 'django.core.mail.backends.dummy.EmailBackend'

This backend is not intended for use in production -- it is provided as a
convenience that can be used during development.

.. _topic-custom-email-backend:

Defining a custom email backend
-------------------------------

If you need to change how emails are sent you can write your own email
backend. The :setting:`EMAIL_BACKEND` setting in your settings file is then
the Python import path for your backend class.

Custom email backends should subclass ``BaseEmailBackend`` that is located in
the ``django.core.mail.backends.base`` module. A custom email backend must
implement the ``send_messages(email_messages)`` method. This method receives a
list of :class:`~django.core.mail.EmailMessage` instances and returns the
number of successfully delivered messages. If your backend has any concept of
a persistent session or connection, you should also implement the ``open()``
and ``close()`` methods. Refer to ``smtp.EmailBackend`` for a reference
implementation.

.. _topics-sending-multiple-emails:

Sending multiple emails
-----------------------

Establishing and closing an SMTP connection (or any other network connection,
for that matter) is an expensive process. If you have a lot of emails to send,
it makes sense to reuse an SMTP connection, rather than creating and
destroying a connection every time you want to send an email.

There are two ways you tell an email backend to reuse a connection.

Firstly, you can use the ``send_messages()`` method. ``send_messages()`` takes
a list of :class:`~django.core.mail.EmailMessage` instances (or subclasses),
and sends them all using a single connection.

For example, if you have a function called ``get_notification_email()`` that
returns a list of :class:`~django.core.mail.EmailMessage` objects representing
some periodic email you wish to send out, you could send these emails using
a single call to send_messages::

    from django.core import mail
    connection = mail.get_connection()   # Use default email connection
    messages = get_notification_email()
    connection.send_messages(messages)

In this example, the call to ``send_messages()`` opens a connection on the
backend, sends the list of messages, and then closes the connection again.

The second approach is to use the ``open()`` and ``close()`` methods on the
email backend to manually control the connection. ``send_messages()`` will not
manually open or close the connection if it is already open, so if you
manually open the connection, you can control when it is closed. For example::

    from django.core import mail
    connection = mail.get_connection()

    # Manually open the connection
    connection.open()

    # Construct an email message that uses the connection
    email1 = mail.EmailMessage('Hello', 'Body goes here', 'from@example.com',
                              ['to1@example.com'], connection=connection)
    email1.send() # Send the email

    # Construct two more messages
    email2 = mail.EmailMessage('Hello', 'Body goes here', 'from@example.com',
                              ['to2@example.com'])
    email3 = mail.EmailMessage('Hello', 'Body goes here', 'from@example.com',
                              ['to3@example.com'])

    # Send the two emails in a single call -
    connection.send_messages([email2, email3])
    # The connection was already open so send_messages() doesn't close it.
    # We need to manually close the connection.
    connection.close()


Testing email sending
=====================

There are times when you do not want Django to send emails at
all. For example, while developing a Web site, you probably don't want
to send out thousands of emails -- but you may want to validate that
emails will be sent to the right people under the right conditions,
and that those emails will contain the correct content.

The easiest way to test your project's use of email is to use the ``console``
email backend. This backend redirects all email to stdout, allowing you to
inspect the content of mail.

The ``file`` email backend can also be useful during development -- this backend
dumps the contents of every SMTP connection to a file that can be inspected
at your leisure.

Another approach is to use a "dumb" SMTP server that receives the emails
locally and displays them to the terminal, but does not actually send
anything. Python has a built-in way to accomplish this with a single command::

    python -m smtpd -n -c DebuggingServer localhost:1025

This command will start a simple SMTP server listening on port 1025 of
localhost. This server simply prints to standard output all email headers and
the email body. You then only need to set the :setting:`EMAIL_HOST` and
:setting:`EMAIL_PORT` accordingly, and you are set.

For a more detailed discussion of testing and processing of emails locally,
see the Python documentation for the :mod:`smtpd` module.