This article, Using a three-folder system to keep e-mail under control in Unclutterer is a good approach to simplying the time it takes to process email. I use this approach and have been for some time. Before I used to try and file my email in different folders, but it just took too much time and it didn’t help me much in locating lost emails. Having less folders is better.
However, before you file it, ask yourself: can I delete this? If you can, do it. That will save you even more time, now and in the future.