A message, such as an email, a discussion group posting, or a comment.
Includes the message title, contents, participants, and other properties.
This is the gd Message kind. See:
http://code.google.com/apis/gdata/common-elements.html#gdMessageKind
These properties are meaningful. They are all optional.
property name property type meaning
-------------------------------------
title string message subject
content string message body
from Contact* sender
to Contact* primary recipient
cc Contact* CC recipient
bcc Contact* BCC recipient
reply-to Contact* intended recipient of replies
link Link* attachment
category Category* tag or label associated with this message
geoPt GeoPt* geographic location the message was posted from
rating Rating* message rating, as defined by the application
* means this property may be repeated.
The Contact properties should be Keys of Contact entities. They are
represented in the XML encoding as linked <gd:who> elements.