Outlook Accelerator improves performance of Outlook by defragmenting large files (Personal Folders) where Outlook stores your emails, attachments, contacts, etc. These files tend to grow relatively fast and being constantly changed by Outlook they usually become hardly fragmented very quickly.

Even if you run a disk defragmenter on a regular basis, Outlook files stay contiguous for just a shot while after the disk defragmentation and then become fragmented again. At the same time Outlook mailbox files may well be as large as 1Gb or even larger. Apparently the less fragmented these files are the better is disk access time and the faster is your Outlook.