a simple scenario could be the following:
The company receives an order via email on the standard email-
account (e.g. info@company.com). That email
will be either manually forwarded to "order entry" or, if the mail
is clearly "identifiable" as an order (e.g because the text string
"order" is found), or automatically forwarded to the person in
charge. This person writes an invoice, prints it out and the
"order entry system" generates a paper output, and a PDF.
Afterwards the "Order entry person " attaches this PDF with
drag and drop from the "Desktop" to the mail and writes for
example an additional note and attaches it as well to the mail.

It would be much better if that step(writing a note) could be
done directly in ZIMBRA (easier than opening an editor, saving
the document and attaching it to the mail)!

Because it could happen, that a mail is routed to different
persons, the person which added the "attachement/note"
and the date should be recognizeable.
I am exited to hear if that killer feature could be soon
integrated. For such a cool feature we would even pay,
(if you are going to support it in feature releases).