It's considered shouting and impolite. I've also seen variations of the Niemann Marcus cookie recipe and Amanda and Greg's school project to send e-mail around the world. These messages are always a hoax and a waste of bandwidth. A lot of people love to forward jokes and humorous stories. E-mail programs vary.
Mailing lists are all different.
Consider whether the reply is appropiate for the entire list or just the person who sent the message. Most high-volume mailing lists have strict guidelines. I don't think that's necessary for the Wordcraft list. If any problems crop up, we can always revise our guidelines.