Message's body can contains styles and other stuff
that can screw the look and feel of digests' mails.
Now we sanitize it if `sanitize_msg_body` is set on the digest (default on).
`force_send` is an option in `mail` core module
that allows to send an email immediately.
Handling the message w/ digest is wrong and in any case
we gonna have a digest w/out the message inside it
since is going to be deleted right after send.
A typical use case is the notification sent to new followers.
When creating digest records within the context of mail composer
(and possibly other contexts) you'll have a `default_template_id`
key in the context which is going to override our safe default.
This is going to break email generation because the template
will be completely wrong and unpredictable. Lesson learned :)
Simone Orsi