The number one most useful piece of advice to dealing with email has been to respond quickly. So I read a lot of things on GTD but didn't end up adopting most

The number one most useful piece of advice to dealing with email has been to respond quickly. So I read a lot of things on GTD but didn't end up adopting most of them. What I did adopt was their rule that if you can respond to or deal with something in less than X minutes (2? 3? forget the number) then do it immediately. This made things so much more manageable and has kept my inbox size down tremendously. Before I found that it had filled up with lots of emails that I knew I should respond to or had to do something to follow up on, but just hadn't yet.