Netiquette, by Virginia Shea, page 52 that a message that was actually written months ago was written today. And using technology to pretend to be somewhere when you're not is inappropriate, no matter who does it. On the other hand, any technique that helps projects stay on schedule deserves consideration in the business world. In any case, smart employees will probably figure out pretty quickly which messages were sent live and which were written months ago. Some companies are now implementing this feature on their corporate email systems.
Bozo filters pose no problem on recreational discussion groups.
But you'd want to be very careful using one on your work email system. Say Joe Schmoe down the hall has a bad habit of sending the Blonde Joke of the Day to everyone on the hallway. Since you're a blonde, you don't appreciate this, and you decide to filter all of Joe's mail. But one day, the department director asks Joe to delegate an important project to you. A better kind of filter allows you to prioritize your mail rather than filtering it completely.