Promote a day for people to delete old emails and empty their trash. I bet it saves many Exabytes of storage and helps speed searches.
Have a national recycling day for emails. MANY emails we get are garbage or daily list mails. I bet if every Yahoo user deleted unimportant emails like sales ads or old conversations and emptied their trash and spam folders just once, it'd save huge amounts of storage on Yahoo and probably speed the system up since searches should improve. Some people already do this diligently but I bet many or even most don't. I try to be good about it but I just saw I have 6000 emails in my inbox. I bet I need to keep about 50 of them. Follow in the footsteps of Hillary Clinton. Start deleting your emails!