Has anyone written an OutOfOffice doo-hickey for Thunderbird and all other mail clients?
It seems to me that it ought to be a straightforward issue, to have a standalone program that interrogates the mail server periodically and matches the contents against a small table.
The table is taken from the spam filter white list (and/or the chosen client’s address books)
Where a sender on the server matches a name in the table, and a "noted" flag is not yet set, set the "Noted" flag and issue a short email to the sender.