##
7.3.2 `Message` objects

class `Message`( | [message])

  A subclass of the `email.Message` module's `Message`. Subclasses of `mailbox.Message` add mailbox-format-specific state and behavior.

  If message is omitted, the new instance is created in a default, empty state. If message is an `email.Message.Message` instance, its contents are copied; furthermore, any format-specific information is converted insofar as possible if message is a `Message` instance. If message is a string or a file, it should contain an RFC 2822-compliant message, which is read and parsed.

The format-specific state and behaviors offered by subclasses vary, but in general it is only the properties that are not specific to a particular mailbox that are supported (although presumably the properties are specific to a particular mailbox format). For example, file offsets for single-file mailbox formats and file names for directory-based mailbox formats are not retained, because they are only applicable to the original mailbox. But state such as whether a message has been read by the user or marked as important is retained, because it applies to the message itself.

There is no requirement that `Message` instances be used to represent messages retrieved using `Mailbox` instances. In some situations, the time and memory required to generate `Message` representations might not not acceptable. For such situations, `Mailbox` instances also offer string and file-like representations, and a custom message factory may be specified when a `Mailbox` instance is initialized.