Managing someone else's inbox - tips?

In my previous employment, I handled my boss's email and one thing I learned right away: there is no easy way to avoid duplication and still keep your boss informed. Here is our system:

1- I did not EVER delete anything. If I had, there would have inevitably been those arguments about, "Where is this?" Instead, I just sorted stuff.

2 - We created three file folders:

1) Junk
2) Personal
2) News

This way, I could pull out items that fell in any of these three categories, leaving the inbox ONLY work-related material. This helped hugely. If this was all I did, it would have been enough to keep him sane when dealing with his inbox. About once a day, he would go through the filed email and empty the folders.

3 - When there was an item he wanted me to take care of, it was flagged a specific color. Once I had taken care of it, it was flagged a different color. Of course, to fully keep your boss in the loop, it's helpful to cc him on your follow up emails of items you are handling. Otherwise, if you don't do this, you need to be extra cautious about setting a specific time to "download" everything you've done and taken care of. If you don't, it's likely that, a week from now, your boss will come into your office in a panic wondering what happened with a specific issue. Avoid that momentary freak out and show him when and how you're doing things. If he decides he doesn't want to see the dup message, you can rethink the strategy.

FYI - If your boss travels a lot and uses a blackberry, the flag system won't work. Keep that in mind and be aware that you'll need to
adjust your system to account for that. My boss would just forward messages to my inbox when he wanted me to take care of things. It was a simple enough solution but, of course, another email in my own flooded inbox ;)

Good luck. I have to tell you that managing my boss's inbox and his calendar where the two most difficult and stressful tasks for me. It's not that it's hard, but everyone has a specific way that they want things done - and many executives are very particular. Try out different methods and see what works.