Awhile ago Microsoft published a hack to increase the filesize limit on Outlook email .PST files. Outlook 2007 had a limit of 20 gigabytes. As email demands grew that limit would be reached rather quickly. The .PST limit was raised in Outlook 2010 and newer to 50 gigabytes which can still be consumed. Below is a capture of the Microsoft information to increase the .PST size for Outlook 2003-2010.
(Click the View FullScreen Button on the upper left of tthe PDF for a good time!)
Warning – this involves some registry editing. If you are not skilled in this please proceed with caution. Working in the Registry is like doing spinal surgery on yourself!
There is an updated version of this information on Microsoft’s site that also covers more recent version of Outlook. Find it at the follwoing Link.