Office Outlook 2007 is slow with pst file greater than 2GB

(Last Updated 29/10/2009, email ashley@csse.uwa.edu.au)

Background Information

This documentation will detail how rectify problems encountered by people who find Office 2007 rather slow where their pst files are equal or greater than 2GB after they changed ie upgraded or installed over from previous Office Versions ie 2003 or earlier.

I’ve found a lot comments and solutions but there not really addressing the problem at hand. You should know that Personal Storage Table format or more commonly PST file is a closed format used for Microsoft for their Outlook clients. There are variations of the PST file ie the earlier formats used ANSI encoding which are limits the PST file to 2GB but the newest version uses UTF-16 encoding which allows PST files up to 20GB. I believe with each subsequent revision of Office hence Outlook there are slight changes to the format ie as mentioned above which may impact the performance of the client.

In my case I had a user who’s PST file was 9GB and was talking up to 6min to load (ie Outlook basically remains unresponsive once you have entered your password to the exchange server no matter if it was cache or online mode). This only happened recently when the person switched to Office 2007. But if you don’t login into the Exchange server you could happily browse your personal PST file which made me wonder.

Solution

It seems when you connect to the Exchange there is some sort of check on the PST file, like a file check of sorts before it would let you read and write to the pst file while connected to exchange.

The solution is simple, you have to export the existing PST file, Delete the old PST file and replace it with the exported PST file.

Ie go to the top of the Mailbox or Personal Folder, then click on

File -> Import and Export -> Export to a file -> Personal Folder File (.pst)

It depend on what version of Outlook you have if you have Outlook 2007, when you export it, the pst file format is Outlook2007 compliant and not work with earlier versions of Office.

Office 2007 PST seems significantly different to earlier Offices including Office 2003, the reason I say this that the 9GB PST file exported from Office 2007 sits at 10.9GB which holds the same exact information just reorganized in the Office 2007 PST format. So there must be a lot of padding or optimizations in the new Office 2007 PST file.

Once exported you should remove the reference to that old format pst file and add the new one in. You can do this by

1. Go to Windows Control Panel

2. Click on Mail

3. Click on the Data Files

4. Click add -> and select where the Outlook 2007 PST compliant file you exported

5. Set the new Outlook 2007 PST as the default Data file

6. Click on the old Outlook PST file and click remove (Just removes it, it doesn’t delete it physically)

7. Rerun Outlook (It dropped down from 6min to 15 seconds)

This solution will be most relevant to people who has moved to Office 2007 but used an existing PST file from previous Office including 2003 who’s personal PST file is greater than 2GB.