Here is my current code for automatic fcc via the `auto-fcc' bbdb field.
It now happens both at mail-setup time, so it works in replies and such,
and at mail-abbrev expansion time.
(defun bbdb/auto-fcc-by-net (net)
(let ((folder (bbdb-record-getprop (bbdb-search-simple nil net)
'auto-fcc)))
(if folder
(mail-fcc (expand-file-name folder vm-folder-directory)))))
(add-hook 'after-load-alist
'("bbdb-com"
(insert-hooks 'bbdb-mail-abbrev-expand-hook nil
'after-bbdb-mail-abbrev-expand-hook)))
(add-hook 'after-bbdb-mail-abbrev-expand-hook 'bbdb/mail-abbrev-auto-fcc)
(defun bbdb/mail-abbrev-auto-fcc ()
(mapcar 'bbdb/auto-fcc-by-net records))
(add-hook 'mail-setup-hook 'bbdb/mail-auto-fcc)
(defun bbdb/mail-auto-fcc ()
(let ((to (mail-fetch-field "to" nil t)))
(if to
(mapcar 'bbdb/auto-fcc-by-net (rfc822-addresses to)))))
