I submit that spam filters should be under the sole control of their end users. If I'm using a Yahoo or Gmail account (I'm not) I should have the option to disable the spam filter entirely, or to only use personal parameters that are trained on the mail only I received, and not email should ever be summarily blackholed without letting me know in some way. If an email bounces, the sender should know. If it's just filtered, it should be in the recipient's spam folder.