You may have noticed that all of your Outlook folders are located under one top-level folder, called Personal Folders. (This may not be the case if you are using Microsoft Exchange Server.) You can look at the photo below for an example of how personal folders look in Outlook.

 

Outlook stores all of your data (except rules, e-mail account settings, and interface customizations) in a personal folder file. This file always has a .pst extension, and can only be opened by Microsoft Outlook.

 

The personal folder file in Outlook 2003 has changed radically from previous versions. The structure of the file itself has changed to reduce file corruption. (The new structure uses Unicode encoding, so you may hear the file referred to as a Unicode .pst. The earlier personal folder files are referred to as ANSII .psts.) This change gives you more storage space in Outlook. In previous versions, your personal folder file started to corrupt around 1.8 gigabytes; the official size limit was 2 gigabytes. When Outlook was first created in 1997, this was an enormous amount of space. Today, obviously, that’s not the case. So, with the new encoding structure, the new personal folder file is limited only by the file system on your computer. It should hold ten times the amount of the space as an older file: 20 gigabytes. Now that’s a lot of space!