I think that the difference is that the RIAA can't look at your GMail account, so they can't know that you have that MP3. Therefore, they will not file a takedown notice.

BUT... (there's always a but =P ), what happens if you upload a video to YouTube, and you save it also in your gmail.

If someone files a takedown notice on that video, should google also delete from your email ? should they also delete it from every other gmail account that holds a copy of that video? Oh man, this is getting complicated...

He meant that you've downloaded the video file and attached it to some email in gmail.

Exactly. Thanks for making it clear.

Files in your gmail are not public. Likewise, files in your Dropbox are not necessarily public. I don't see the problem with removing public links in response to a DMCA takedown, while still allowing private access for those people who uploaded it.

The difference is Goole's relationship with the music industry - this has nothing to do with laws and everything to do with Google's ability to set the agenda.