I 'Archive' e-mails once I consider whatever they pertain to to be dealt with. I also have a folder called 'Receipts' which is where I put any e-mail which is an automated confirmation, like order confirmations, receipts and despatch notifications. My inbox therefore has very little in it -- and if it's empty then I'm happy because it means I have no outstanding ******** to deal with -- yet I don't spend much time organising things into various folders, sub-folders and so on. Once I've replied or dealt with the matter, I click 'Archive' and it's filed away for me.