[ajross]

Again, that's not the structure of the law. The DMCA requires that a takedown notice specify the specific content. Both the data itself and the usage have to be identified, there's no notion in the law of forbidding access to specific "files" by their data alone.

[zokier]

Yes, Dropbox is working pre-emptively on their own initiative here.

The message is quite cleverly constructed, as it doesn't actually say that there is a DMCA takedown request against the file (because there isn't). It just says that there has been a takedown request sometime, possibly(probably) against some other file/url.