We link http://sitename/my/preferences in a bunch of places in emails with text similar to: "To change your preferences click: http://sitename/my/preferences.
If a user is not logged in clicking on that link takes you to a 404, this can be very confusing, especially for mailing list migrations.
Instead we should have a special /my/preferences page for anon that explains they are not logged in and provides instructions on how to log in.
cc @eviltrout
