Friends want to show that they care. They show that they care by forwarding you a funny story, a virus warning, or a photo that they enjoyed. They show that they care by sending a mass email using the “To:” field and so exposing your email address to a bunch of strangers.
The next time your friend displays less-than-acceptable consideration when emailing you, how about sending them the following response…
Please visit http://thanksno.com/
It’s because I like getting personal messages from you, but don’t want any more email like this, please.