The first rule is to keep stuff out of your in box that you don't need to waste time on. Use the junk mail filters on your mail system to the fullest. Check the junk mail folder once a day or so for anything you really do need, and empty the rest. The way I check mine is to sort by the subject line, which allows me to quickly see any legitimate emails.
In addition to the junk mail filters, use the "rules" function if you are in Outlook. Under the "tools" menu, select "rules and alerts." You can fairly easily set rules to send messages from Bill to Sue for action, or to file all messages about the "picnic" into a "picnic" folder. You can also create rules by right-clicking on a message in the in box and selecting "create rule."
Even with the best filters and rules, stuff you don't need will still end up in your in box. Don't dally - delete! And if a message has been in your in box more than a week or so without you taking any action on it - delete! If it hasn't happened yet, it probably won't.
For those messages that are legitimate and require some sort of action, decide whether you or someone else is the right person to deal with it. Are you really the best person to handle this message? Could someone on your team learn by handling it instead? Unless only you can do it, delegate it!
If a message requires action that only you can take, decide if it must be done now or can be deferred. If it can be deferred, right click on the message, select "move to folder" and move it to the tasks folder. Set a reminder date for the date you plan to work on it.
If a message requires action or a response urgently, and if it is mission critical, and if you can complete the action or response in a minute or two, then do it NOW. If those three conditions do not all exist, choose one of the options above.
Some messages may not require action or response, but contain data or other information you want to keep. In that case, deposit the message in a file and get it out of your in box. I save that sort of message to a my Windows file system, rather than in Outlook itself. With the message selected, choose "file>save as." Give it a location and a name you will remember.
The seventh D
The seventh D is really the first D - DECIDE. Don't let messages languish in your in box. Decide - on your first reading of the message - whether you will Dodge (add the sender to the junk list), Delete, Delegate, Defer, Do or Deposit.
Let me know how it goes!