As mentioned on a past Post (LINK) as the size of the Outlook data file grows Outlook will begin to slow down. Here are tips using the Advanced Find feature to quickly free up the most space from Outlook:
May 2011 archive
Have you noticed Outlook is running slower? Check the size of your PST file. The PST file is a file used by Outlook to store all the data in outlook (mail messages, Contacts, Calendar entries and Tasks). When this file starts to get very large Outlook will begin to slow down.