To reduce the size of your Outlook Data File (.pst) or Offline Outlook Data File (.ost), you can manually compact the data file. Select your version of Outlook below to see instructions on how to reduce the size of a .pst or .ost file. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.