These five easy steps will help you establish an e-mail filing system that allows you to efficiently process and access e-mails. Use one or more of the following methods to get organized.

1. File By Client Name
If your work involves a lot of different clients so it makes sense to make folders for each customer; for example: Client A, B, and C. If you have hundreds of them, you can categorize them, creating general folders for each one; for example: Retail clients, Banking clients, and Healthcare clients.

2. File By Product or Service
If your work deals more with products and services, make general folders for all the main product and service categories. Within these folders, you can put all your related files and add subfolders for the product or service category.

3. File By Project
Perhaps you might prefer to base your filing system on projects, in which you create folders for each major projects you are working on. You can also add the dates to see which is more recent or important and such. Under each project file, you can also add subfolders for each different task; for example under the project "New Web Site", you can have the following subfolders: design, notes, management, etc.

4. Take Advantage of Automated Filing.

Microsoft Outlook, Entourage and Apple Mail have features for automatically assigning e-mails, from specific senders or about certain subjects, to pre-assigned folders. E-mails then show up in your main box list, but are also filed under their specific topic.

5. When New E-Mails Come In, Don't Let Them Linger In Your Mailbox
When you get a new message, either; reply immediately if possible, delete the message if you don't need it, forward if you have to, or file the message in the appropriate folder.
Don't ignore your messages, and don't let them clutter your inbox.

Source: Five Easy Steps To E-Mail Organization [The Huffington Post]