def mark_read(user, message):
BackendClass = stored_messages_settings.STORAGE_BACKEND<EOL>backend = BackendClass()<EOL>backend.inbox_delete(user, message)<EOL>
Mark message instance as read for user.
Returns True if the message was `unread` and thus actually marked as `read` or False in case
it is already `read` or it does not exist at all.

:param user: user instance for the recipient
:param message: a Message instance to mark as read