While the term is very generic, "ContentScanner" usually refers to tools that integrate with an [MTA] and scan [Email] on-the-fly as it arrives or goes out. They can be configured to react to [Email] in any number of ways depending on headers, body text, attachment types or filenames, and so on. The most common use is to hook anti-[Virus] and anti-[Spam] tools into the mail sending and delivery process, but they can also drive (selective or not) automated archiving or backup tools, gather statistics, or do just about anything you can think of. Depending on configuration and how they integrate with the [MTA] of choice they may be able to scan only locally-sent or -received [Email] or also messages being relayed.