Comment 2 for bug 1265882

mail.mail has a mail.message embedded (encapsulated / as a child)

_inherits = {'mail.message': 'mail_message_id'}

http://bazaar.launchpad.net/~openerp/openobject-addons/trunk/view/head:/mail/mail_mail.py#L42

This makes me consider that if you create a mail.message an optional mail.mail can be made as a parent and this would serve to store more details about the actual mail message (instead of just the content) and how it got delivered or should be sent.

This would server to keep the mail.message agnostic of the source, allowing users to enter messages without having to have one model that needs more columns to store all the possible meta data associated with real SMTP/IMAP/POP3 protocols.