+(defun message-headers-to-generate (headers included-headers excluded-headers)
+ "Return a list that includes all headers from HEADERS.
+If INCLUDED-HEADERS is a list, just include those headers. If if is
+t, include all headers. In any case, headers from EXCLUDED-HEADERS
+are not included."
+ (let ((result nil)
+ header-name)
+ (dolist (header headers)
+ (setq header-name (cond
+ ((and (consp header)
+ (eq (car header) 'optional))
+ ;; On the form (optional . Header)
+ (cdr header))
+ ((consp header)
+ ;; On the form (Header . function)
+ (car header))
+ (t
+ ;; Just a Header.
+ header)))
+ (when (and (not (memq header-name excluded-headers))
+ (or (eq included-headers t)
+ (memq header-name included-headers)))
+ (push header result)))
+ (nreverse result)))
+