When it has found a parent, it returns the corresponding group name. It
is recommended that you set @code{nnmail-message-id-cache-length} to a
somewhat higher number than the default so that the message ids are
-still in the cache. (A value of 5000 appears to create a file some
-300 kBytes in size.)
+still in the cache. (A value of 5000 appears to create a file some 300
+kBytes in size.) When @code{nnmail-cache-accepted-message-ids} is
+non-nil, Gnus also records the message ids of moved articles, so that
+the followup messages goes into the new group.
@node Group Mail Splitting