Corrupt OST files in Outlook 2007

We are having an increase in the number of corrupt ost files with our users who are using the Outlook client in cached mode.  We are currently running Exchange Server 2003 SP2 and Outlook 2007 SP2.  We were running Office 2003 and upgraded to Office 2007 in August of 2009.  Everything was working great until the beginning of December 2009. We started receiving help desk calls about users being unable to access their mailboxes via the Outlook client.  They were receiving the error "the file C:\Documents and Settings\<username>\Local Settings\Application Data\Microsoft\Outlook\outlook.ost is not a personal folders file."

The frequency has been increasing over the past several months (over 100 trouble tickets with only 400 users located in this office) with no real pattern and we are unable to find a true fix.  We have found many articles on the Inbox repair tool, and it will work sometimes, but not always...and never permanently.  Needless to say, users are becoming frustrated.  As a quick fix, we have been deleting the corrupted ost file and letting Outlook recreate it, but we would really like to find out why it is happening.  What is even more frustrating is that we may fix one user’s ost, only to have it corrupted the next day or worse yet, several hours later.  Some mailboxes are over 2GB which we have read can lead to corruption, but most are only 100MB to 500MB in size.  Has anyone heard of anything similar to this or about anyone else that has been experiencing this issue?  Are there any service packs or hotfixes that anyone is aware of that might have caused it?  Any help is greatly appreciated.
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HI, indeed OST (and PST) files have many trouble when there are near 2 GB capacity, for these cases I suggest to make a PST file for the old mails, and then delete them from the exchange, so that the OST file become smaller (and the data file in your Exchange too).

Which OS are they using? I really don´t think is a service pack or actualization problem

This sounds like networking issues.

OST file corruption can occur if theeir are communication issues with the exchange server.  It can also be caused by abnormal closure of outlook or by malicious software activity.  The error you have described can be caused by sychronisation problems with the exchange server.  Check for frequent disconnects etc between the clients and the server which may indicate communication problems.  Try disabling cached mode if possible and see if it is more reliable.  Also check that users are closing oultlook gracefully.
Since you have upgraded from Office 2003 to 2007, please see the below Technet article for some of the most common Outlook issues. Hope it helps you determine the casue of the issue that you have.
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aiuWebServicesAuthor Commented:
The OS is Windows XP SP3.  I don't think it's a service pack or hotfix either since not everyone is experiencing it.

Thank you for the great suggestions.  I had started disabling cached mode on clients that had a lot of problems and it has helped, but there are a lot of desktops to touch.  I will look into the connectivity on clients that are still in cached mode and also inquire about how they shut down Outlook.
Have you checked whether the corrupt OST file is in old Outlook 97-2002 format or in new Outlook 2003/2007 format?

Since you are using Outlook 2003 and then upgraded to Outlook 2007, by default, the new .OST file created by Outlook 2003/2007 is in the new Outlook 2003/2007 format which do NOT have 2GB file size limit anymore. (It seems that the small file in several hundreds of MB is also corrupt confirm this).

I think the problem may be with some updates of Outlook 2007. We have found there are bugs in some versions of Outlook 2007 but not in Outlook 2003. Maybe in Dec, 2009, your customer's system is automatically upgraded(with Windows Auto Update) to a new update of Outlook 2007 which has potiential problems. Have you contacted Microsoft and seek for possible solutions?

If the .OST file is corrupt, sometimes the Inbox Repair Tool can help. If not, then you can resort to some third party tools such as Advanced Exchange Recovery at and Advanced Outlook Repair at , they can recover data from OST or PST files when they are corrupt. Note these tools will take a long time if your files are large(for example, 18GB)


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Here is my suggestion with your problem, create PSTs and have the users copy their email to those personal folders. Or you can setup auto-archive, either way you want to bring the ost file to a smaller size.

Also another question...

Why are you using cache exchange mode?

Have you also tried to use offline folders?
aiuWebServicesAuthor Commented:
Thank you for all the help so far.  We have tried many of your suggestions, but just had another corrupt ost this morning.

Chcw, in regards to the OST file format, it should be in the new Outlook 2003/2007 format since we've never been on any other version.  We are going to open a support call with Microsoft to see if they can help.

Adam, we do have some users that have created PSTs and have moved their mail into them.  Our biggest fear with those is if something happens to their computer (hard drive failure) and they lose their mail.  As far as cached mode...we used to be a Novell shop and had a consulting group come in and help with the migration to Exchange.  During the migration we set everyone up with cached mode and it's been like that ever since.  We have not tried offline folders.  I will look into that.

Thanks again.  I will keep everyone posted on our progress.
I agree coping the PST to the hard drive and the hard drive would happen to crash that could be a problem. Do you have the option to copy the PST to a file server that can be backed up regularly?
aiuWebServicesAuthor Commented:
I apologize for not updating this, but I've been playing phone tag with a technician from Microsoft.  I'm hoping to touch base with him today.
aiuWebServicesAuthor Commented:
I contacted Microsoft support, and it ended up being a problem with Diskkeeper's new Intelliwrite feature.  We disabled the feature, and the OST corruption has ended.
aiuWebServicesAuthor Commented:
You recommended that we contact Microsoft and they were able to find a solution.
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