I have noticed there is new 'Archive' button in the yahoo mail top at the location used to be for 'Delete' button. This caused several mistakes on me which a mail intended to be deleted ended up in the 'Archive' folder. You may want to force your users to be aware of this new button, but it is a bad user experience decision. If you do care your user experience, please restore the 'Delete' button to old location. After all, a big portion of daily received emails should be deleted instead of being archived.