But then they also won't know that the folders aren't quite like an email interface either. I mean, at some point users have to learn what the stuff on a website they use does and what the things are, and sure it helps if the interface is clear and makes sense and is like other sites, but I don't think any of your suggestions is truly simpler or explains better than having a delete button. That button you expect to delete whatever it is you see on the screen that you put a checkmark on. Which in this case is messages in your inbox. To me that seems fairly transparent, and I'm unconvinced that this ambiguity truly exists for many new users, and that even if it does it is worse than having a delete button not named "delete" like they are everywhere would be.