[Windflier]

I'm thinking the client in this case is the email sender who can tell that you, as the recipient have opened it. The recipient can't do anything about it and wouldn't even know that it happened.

That's exactly how I understand the article. This is a function that operates from the sender's end, and allows them to know what you've done with the mail they've sent you without your express knowledge.

Very creepy stuff.

[tomkat]