Reducing OST file sizes but maintain access to content

We are using Office365 hosted Exchange (Rackspace) with Outlook 2016 desktop clients.

Several of our top executives and key employees have very large OST files which affect the performance of the Outlook client.  At the same time, they do not want to delete mail and want to maintain accessibility to all of their messages.  I have had (as most) bad experiences with PST archive files becoming corrupt and do not want to utilize them as a solution.

Does anyone have a solution for maintaining access while reducing the size of the OST file sizes.  Are their recommended 3rd party apps that integrate fully with Outlook?  What about apps that automatically store attached files in the file system rather than as part of the OST file?

Any help would be appreciated.


TimIT DirectorAsked:
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Brian BEE Topic Advisor, Independant Technology ProfessionalCommented:
You could find out if your mail provider supports archiving. This would allow a separate folder that is actually stored offline unless needed.

There are also third party tools that will store attachments separate from the Exchange database, but I have a feeling that these all are designed to run on the server.

You also might delete their OST and see if it is any smaller when Outlook recreates it.

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David Johnson, CD, MVPOwnerCommented:
You could uncheck Use Cached Exchange Mode or reduce the Mail to Keep offline from ALL to say 1 year. The only difference to the user is that items older than a year will have to be fetched from the server and not stored offline
Todd NelsonSystems EngineerCommented:
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Brian BEE Topic Advisor, Independant Technology ProfessionalCommented:
I think what Todd is trying to say is that an alternative is to use Outlook Web Access instead of Outlook.
Mohammad Ishtyaq khatriSr. Systems EngineerCommented:
Adjust the offline mail setting as required from the control panel. This will help reduce the OST Size. But, In case of those existing OST's you will have to Close the outlook and rename the OST for it to generate new OST's based on the chosen preferred days.
I am confused, if you are using Rackspace hosted exchange, probably you should not get O365


if you are sure that you have got O365 subscription through rack space, then you can ask for O365 EXO online archival from them which will allow mails to be archived manually / with predefined retention policies and archival will get connected to OWA and outlook while you have internet connectivity. This archival don't need OST file as well and remain accessible as long as internet is ON
Marshal HubsEmail ConsultantCommented:
Check following link to reduce OST file size:
Sandeep KumarAssociate ConsultantCommented:
You can reduce the size of OST file and sort errors by 3 methods;
1. By disabling add-ins
2. Archiving OST file data
3. Compressing Outlook data file.
Look into for details for reducing the OST file size with access to its content.
Brian BEE Topic Advisor, Independant Technology ProfessionalCommented:
I said recreate the OST file rather than compact it per those vendor links, because compact doesn't work as well. Plus one of the requirements was to keep all information and not have to delete anything.
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