-Whitelists}), but uses the BBDB as the source of whitelisted addresses,
-without regular expressions. You must have the BBDB loaded for
-@code{spam-use-BBDB} to work properly. Only addresses in the BBDB
-will be allowed through; all others will be classified as spam.
+Whitelists}), but uses the BBDB as the source of whitelisted
+addresses, without regular expressions. You must have the BBDB loaded
+for @code{spam-use-BBDB} to work properly. Messages whose senders are
+not in the BBDB will be sent to the next spam-split rule. This is an
+explicit filter, meaning that unless someone is in the BBDB, their
+messages are not assumed to be spam or ham.
+
+@end defvar
+
+@defvar spam-use-BBDB-exclusive
+
+Set this variable to @code{t} if you want to use the BBDB as an
+implicit filter, meaning that every message will be considered spam
+unless the sender is in the BBDB. Use with care. Only sender
+addresses in the BBDB will be allowed through; all others will be
+classified as spammers.