Keep getting strange Japanese Langauge emails from ''Dropbox''. I cannot block these people and they send me several emails a day. Please Help.

 

How can I block these people ??

I've read on the forum that it is not possible to sync a Microsoft Identity using Dropbox, but is it possible simply to back up a Microsoft Identity using Dropox, without syncing to another computer? 

It would just be good to know that I do have an online backup in Dropbox for the one computer that I do use. 

Thanks.