Source code: Lib/email/__init__.py

The email package is a library for managing email messages, including MIME and other RFC 2822-based message documents. It is specifically not designed to do any sending of email messages to SMTP (RFC 2821), NNTP, or other servers; those are functions of modules such as smtplib and nntplib. The email package attempts to be as RFC-compliant as possible, supporting in addition to RFC 2822, such MIME-related RFCs as RFC 2045, RFC 2046, RFC 2047, and RFC 2231.

The primary distinguishing feature of the email package is that it splits the parsing and generating of email messages from the internal object model representation of email. Applications using the email package deal primarily with objects; you can add sub-objects to messages, remove sub-objects from messages, completely re-arrange the contents, etc. There is a separate parser and a separate generator which handles the transformation from flat text to the object model, and then back to flat text again. There are also handy subclasses for some common MIME object types, and a few miscellaneous utilities that help with such common tasks as extracting and parsing message field values, creating RFC-compliant dates, etc.

The following sections describe the functionality of the email package. The ordering follows a progression that should be common in applications: an email message is read as flat text from a file or other source, the text is parsed to produce the object structure of the email message, this structure is manipulated, and finally, the object tree is rendered back into flat text.

It is perfectly feasible to create the object structure out of whole cloth — i.e. completely from scratch. From there, a similar progression can be taken as above.

Also included are detailed specifications of all the classes and modules that the email package provides, the exception classes you might encounter while using the email package, some auxiliary utilities, and a few examples. For users of the older mimelib package, or previous versions of the email package, a section on differences and porting is provided.

Contents of the email package documentation:

See also

Module smtplib
SMTP protocol client
Module nntplib
NNTP protocol client

19.1.15. Package History

This table describes the release history of the email package, corresponding to the version of Python that the package was released with. For purposes of this document, when you see a note about change or added versions, these refer to the Python version the change was made in, not the email package version. This table also describes the Python compatibility of each version of the package.

email version distributed with compatible with
1.x Python 2.2.0 to Python 2.2.1 no longer supported
2.5 Python 2.2.2+ and Python 2.3 Python 2.1 to 2.5
3.0 Python 2.4 and Python 2.5 Python 2.3 to 2.6
4.0 Python 2.5 to Python 2.7 Python 2.3 to 2.7
5.0 Python 3.0 and Python 3.1 Python 3.0 to 3.2
5.1 Python 3.2 Python 3.2

After Version 5.1 (Python 3.2), the email package no longer has a version that is separate from the Python version. (See the What’s New in Python documents for the respective Python versions for details on changes.)

Here are the major differences between email version 5.1 and version 5.0:

  • It is once again possible to parse messages containing non-ASCII bytes, and to reproduce such messages if the data containing the non-ASCII bytes is not modified.
  • New functions message_from_bytes() and message_from_binary_file(), and new classes BytesFeedParser and BytesParser allow binary message data to be parsed into model objects.
  • Given bytes input to the model, get_payload() will by default decode a message body that has a Content-Transfer-Encoding of 8bit using the charset specified in the MIME headers and return the resulting string.
  • Given bytes input to the model, Generator will convert message bodies that have a Content-Transfer-Encoding of 8bit to instead have a 7bit Content-Transfer-Encoding.
  • New class BytesGenerator produces bytes as output, preserving any unchanged non-ASCII data that was present in the input used to build the model, including message bodies with a Content-Transfer-Encoding of 8bit.

Here are the major differences between email version 5.0 and version 4:

  • All operations are on unicode strings. Text inputs must be strings, text outputs are strings. Outputs are limited to the ASCII character set and so can be encoded to ASCII for transmission. Inputs are also limited to ASCII; this is an acknowledged limitation of email 5.0 and means it can only be used to parse email that is 7bit clean.

Here are the major differences between email version 4 and version 3:

  • All modules have been renamed according to PEP 8 standards. For example, the version 3 module email.Message was renamed to email.message in version 4.

  • A new subpackage email.mime was added and all the version 3 email.MIME* modules were renamed and situated into the email.mime subpackage. For example, the version 3 module email.MIMEText was renamed to email.mime.text.

    Note that the version 3 names will continue to work until Python 2.6.

  • The email.mime.application module was added, which contains the MIMEApplication class.

  • Methods that were deprecated in version 3 have been removed. These include Generator.__call__(), Message.get_type(), Message.get_main_type(), Message.get_subtype().

  • Fixes have been added for RFC 2231 support which can change some of the return types for Message.get_param and friends. Under some circumstances, values which used to return a 3-tuple now return simple strings (specifically, if all extended parameter segments were unencoded, there is no language and charset designation expected, so the return type is now a simple string). Also, %-decoding used to be done for both encoded and unencoded segments; this decoding is now done only for encoded segments.

Here are the major differences between email version 3 and version 2:

  • The FeedParser class was introduced, and the Parser class was implemented in terms of the FeedParser. All parsing therefore is non-strict, and parsing will make a best effort never to raise an exception. Problems found while parsing messages are stored in the message’s defect attribute.
  • All aspects of the API which raised DeprecationWarnings in version 2 have been removed. These include the _encoder argument to the MIMEText constructor, the Message.add_payload() method, the Utils.dump_address_pair() function, and the functions Utils.decode() and Utils.encode().
  • New DeprecationWarnings have been added to: Generator.__call__(), Message.get_type(), Message.get_main_type(), Message.get_subtype(), and the strict argument to the Parser class. These are expected to be removed in future versions.
  • Support for Pythons earlier than 2.3 has been removed.

Here are the differences between email version 2 and version 1:

  • The email.Header and email.Charset modules have been added.

  • The pickle format for Message instances has changed. Since this was never (and still isn’t) formally defined, this isn’t considered a backward incompatibility. However if your application pickles and unpickles Message instances, be aware that in email version 2, Message instances now have private variables _charset and _default_type.

  • Several methods in the Message class have been deprecated, or their signatures changed. Also, many new methods have been added. See the documentation for the Message class for details. The changes should be completely backward compatible.

  • The object structure has changed in the face of message/rfc822 content types. In email version 1, such a type would be represented by a scalar payload, i.e. the container message’s is_multipart() returned false, get_payload() was not a list object, but a single Message instance.

    This structure was inconsistent with the rest of the package, so the object representation for message/rfc822 content types was changed. In email version 2, the container does return True from is_multipart(), and get_payload() returns a list containing a single Message item.

    Note that this is one place that backward compatibility could not be completely maintained. However, if you’re already testing the return type of get_payload(), you should be fine. You just need to make sure your code doesn’t do a set_payload() with a Message instance on a container with a content type of message/rfc822.

  • The Parser constructor’s strict argument was added, and its parse() and parsestr() methods grew a headersonly argument. The strict flag was also added to functions email.message_from_file() and email.message_from_string().

  • Generator.__call__() is deprecated; use Generator.flatten instead. The Generator class has also grown the clone() method.

  • The DecodedGenerator class in the email.generator module was added.

  • The intermediate base classes MIMENonMultipart and MIMEMultipart have been added, and interposed in the class hierarchy for most of the other MIME-related derived classes.

  • The _encoder argument to the MIMEText constructor has been deprecated. Encoding now happens implicitly based on the _charset argument.

  • The following functions in the email.Utils module have been deprecated: dump_address_pairs(), decode(), and encode(). The following functions have been added to the module: make_msgid(), decode_rfc2231(), encode_rfc2231(), and decode_params().

  • The non-public function email.Iterators._structure() was added.

19.1.16. Differences from mimelib

The email package was originally prototyped as a separate library called mimelib. Changes have been made so that method names are more consistent, and some methods or modules have either been added or removed. The semantics of some of the methods have also changed. For the most part, any functionality available in mimelib is still available in the email package, albeit often in a different way. Backward compatibility between the mimelib package and the email package was not a priority.

Here is a brief description of the differences between the mimelib and the email packages, along with hints on how to port your applications.

Of course, the most visible difference between the two packages is that the package name has been changed to email. In addition, the top-level package has the following differences:

The Message class has the following differences:

  • The method asString() was renamed to as_string().
  • The method ismultipart() was renamed to is_multipart().
  • The get_payload() method has grown a decode optional argument.
  • The method getall() was renamed to get_all().
  • The method addheader() was renamed to add_header().
  • The method gettype() was renamed to get_type().
  • The method getmaintype() was renamed to get_main_type().
  • The method getsubtype() was renamed to get_subtype().
  • The method getparams() was renamed to get_params(). Also, whereas getparams() returned a list of strings, get_params() returns a list of 2-tuples, effectively the key/value pairs of the parameters, split on the '=' sign.
  • The method getparam() was renamed to get_param().
  • The method getcharsets() was renamed to get_charsets().
  • The method getfilename() was renamed to get_filename().
  • The method getboundary() was renamed to get_boundary().
  • The method setboundary() was renamed to set_boundary().
  • The method getdecodedpayload() was removed. To get similar functionality, pass the value 1 to the decode flag of the get_payload() method.
  • The method getpayloadastext() was removed. Similar functionality is supported by the DecodedGenerator class in the email.generator module.
  • The method getbodyastext() was removed. You can get similar functionality by creating an iterator with typed_subpart_iterator() in the email.iterators module.

The Parser class has no differences in its public interface. It does have some additional smarts to recognize message/delivery-status type messages, which it represents as a Message instance containing separate Message subparts for each header block in the delivery status notification [1].

The Generator class has no differences in its public interface. There is a new class in the email.generator module though, called DecodedGenerator which provides most of the functionality previously available in the Message.getpayloadastext() method.

The following modules and classes have been changed:

  • The MIMEBase class constructor arguments _major and _minor have changed to _maintype and _subtype respectively.

  • The Image class/module has been renamed to MIMEImage. The _minor argument has been renamed to _subtype.

  • The Text class/module has been renamed to MIMEText. The _minor argument has been renamed to _subtype.

  • The MessageRFC822 class/module has been renamed to MIMEMessage. Note that an earlier version of mimelib called this class/module RFC822, but that clashed with the Python standard library module rfc822 on some case-insensitive file systems.

    Also, the MIMEMessage class now represents any kind of MIME message with main type message. It takes an optional argument _subtype which is used to set the MIME subtype. _subtype defaults to rfc822.

mimelib provided some utility functions in its address and date modules. All of these functions have been moved to the email.utils module.

The MsgReader class/module has been removed. Its functionality is most closely supported in the body_line_iterator() function in the email.iterators module.

Footnotes

[1]Delivery Status Notifications (DSN) are defined in RFC 1894.