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Outlook XP and earlier have a limit of 2gigabytes on the size of its PST file. However there's no warning, only problems, if you exceed that limit.
My PST has grown over 2gig, and now I can't repair it. What do I do?
In an earlier article, What can I do about Outlook's huge PST? I discussed how to use multiple PSTs and other techniques to manage the size of Outlook's email personal storage files, known as PST files. That article was mostly about the inconvenience of managing large files, and mentioned in passing that there's a 2 gigabyte limit to Outlook's PST.
As it turns out it is possible to create a PST that's larger than 2 gigabytes. Unfortunately that's where the trouble starts.
The problem manifests when you start Outlook and it complains about the PST, typically instructing you to use the Inbox Repair Tool.
Step one is to do exactly that. You can read more about the Inbox Repair Tool, called scanpst in this Microsoft Knowledgebase Article. If that tool completes successfully and the problem does not reoccur, you should examine the size of your PST and determine if some of the steps in the earlier article are called for.
If scanpst fails and the PST file is at or over 2 gigabytes (2,147,483,648 bytes) in size then you have a problem; you are going to lose some email.
Microsoft has made available an Oversized PST and OST Crop Tool. The crop tool does just that: it crops, or cuts, the size of the PST file by a specified amount to make it smaller. It makes it small enough to run scanpst on which can recover the contents of the PST. Any messages in the portion of the PST that was cut is lost.
The lesson here is to keep an eye on the size of your PST. While it would be nice if Outlook actually prevented PSTs from growing beyond the limits Outlook can handle it may not, and obviously it can result in lost messages. Make sure to have a decent backup strategy and keep an eye on your PST size.