[tytso]

Um, you do realize that pretty much every single mail service provider is "scanning" their customer's email to screen out spam, right? That's also an algorithmic analysis of the body of the e-mail, and it's providing a service that most customers appreciate (since the generally don't want to swamped by hundreds of Viagra and "make money fast" emails every day)

[newman314]

Spam scanning can be thought of a continuous stream without a given email assigned to a user whereas contextual scanning for the purpose of advertisement necessarily ties emails to you.

Maybe it's just a semantic difference but I would argue that that is a sufficiently big differentiator.