Mastering Technical Sales has a great article on their site explaining how to handle 200 emails a day. It is purposely written for suggestions to their target audience which is the pre-sales technical folks that are the brains in the IT sales world.
I pulled out a few of the more relevant paragraphs that were relevant to all regarding of profession but I suggest that you read the entire article.
I will start this suggestion list by sharing one of my habits. “Don’t file – SEARCH”. Install one of the several desktop search indexing tools such as Google Desktop Search, Windows Desktop Search, or Copernic Desktop Search. Then, when you have read and are finished with an email, move it to a “Done” folder and forget about it. Don’t try to figure out if you should file the email in the customer folder, the folder of the person that sent you the email, the folder for product problems or whatever. Most people end up spending way to much time worrying about their filing system or trying to find an email in the file system. Don’t worry about it – just search for the email in one of the above systems let the engine do the heavy lifting for you.