##
7.3.4 Deprecated classes and methods

Older versions of the `mailbox` module do not support modification of mailboxes, such as adding or removing message, and do not provide classes to represent format-specific message properties. For backward compatibility, the older mailbox classes are still available, but the newer classes should be used in preference to them.

Older mailbox objects support only iteration and provide a single public method:

`next`( | )

  Return the next message in the mailbox, created with the optional factory argument passed into the mailbox object's constructor. By default this is an `rfc822.Message` object (see the `rfc822` module). Depending on the mailbox implementation the fp attribute of this object may be a true file object or a class instance simulating a file object, taking care of things like message boundaries if multiple mail messages are contained in a single file, etc. If no more messages are available, this method returns `None`.

Most of the older mailbox classes have names that differ from the current mailbox class names, except for `Maildir`. For this reason, the new `Maildir` class defines a `next()` method and its constructor differs slightly from those of the other new mailbox classes.

The older mailbox classes whose names are not the same as their newer counterparts are as follows:

class `UnixMailbox`( | fp[, factory])

  Access to a classic Unix-style mailbox, where all messages are contained in a single file and separated by "`From` "(a.k.a. "`From_`") lines. The file object fp points to the mailbox file. The optional factory parameter is a callable that should create new message objects. factory is called with one argument, fp by the `next()` method of the mailbox object. The default is the `rfc822.Message` class (see the `rfc822` module - and the note below).

  Note: For reasons of this module's internal implementation, you will probably want to open the fp object in binary mode. This is especially important on Windows.

  For maximum portability, messages in a Unix-style mailbox are separated by any line that begins exactly with the string `'From '` (note the trailing space) if preceded by exactly two newlines. Because of the wide-range of variations in practice, nothing else on the From_ line should be considered. However, the current implementation doesn't check for the leading two newlines. This is usually fine for most applications.

  The `UnixMailbox` class implements a more strict version of From_ line checking, using a regular expression that usually correctly matched From_ delimiters. It considers delimiter line to be separated by "`From name time`" lines. For maximum portability, use the `PortableUnixMailbox` class instead. This class is identical to `UnixMailbox` except that individual messages are separated by only "`From` " lines.

  For more information, see Configuring Netscape Mail on Unix: Why the Content-Length Format is Bad.

class `PortableUnixMailbox`( | fp[, factory])

  A less-strict version of `UnixMailbox`, which considers only the "`From` " at the beginning of the line separating messages. The ``name time'' portion of the From line is ignored, to protect against some variations that are observed in practice. This works since lines in the message which begin with `'From '` are quoted by mail handling software at delivery-time.

class `MmdfMailbox`( | fp[, factory])

  Access an MMDF-style mailbox, where all messages are contained in a single file and separated by lines consisting of 4 control-A characters. The file object fp points to the mailbox file. Optional factory is as with the `UnixMailbox` class.

class `MHMailbox`( | dirname[, factory])

  Access an MH mailbox, a directory with each message in a separate file with a numeric name. The name of the mailbox directory is passed in dirname. factory is as with the `UnixMailbox` class.

class `BabylMailbox`( | fp[, factory])

  Access a Babyl mailbox, which is similar to an MMDF mailbox. In Babyl format, each message has two sets of headers, the original headers and the visible headers. The original headers appear before a line containing only `'*** EOOH ***'` (End-Of-Original-Headers) and the visible headers appear after the `EOOH` line. Babyl-compliant mail readers will show you only the visible headers, and `BabylMailbox` objects will return messages containing only the visible headers. You'll have to do your own parsing of the mailbox file to get at the original headers. Mail messages start with the EOOH line and end with a line containing only `'\037\014'`. factory is as with the `UnixMailbox` class.

If you wish to use the older mailbox classes with the `email` module rather than the deprecated `rfc822` module, you can do so as follows:

    import email
    import email.Errors
    import mailbox

    def msgfactory(fp):
        try:
            return email.message_from_file(fp)
        except email.Errors.MessageParseError:
            # Don't return None since that will
            # stop the mailbox iterator
            return ''

    mbox = mailbox.UnixMailbox(fp, msgfactory)

Alternatively, if you know your mailbox contains only well-formed MIME messages, you can simplify this to:

    import email
    import mailbox

    mbox = mailbox.UnixMailbox(fp, email.message_from_file)