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Outlook Cache Mode | Outlook version 2010, Exchange version 2010. RRS feed

  • Question

  • Hi,

    A mystery on Outlook Cached Mode

    There is no gpo to enabled Exchange Cached Mode to computers. and confirmed that Outlook Cached Mode is disabled in Outlook.

    but upon launching Outlook, an ost file being created in C:\....Outlook folder.

    What is causing the creation of ost file?

    please shed some lights. thank you

    Monday, August 19, 2019 12:07 PM

Answers

  • Hi Perry,

    thanks.

    If the key does not exist, does that mean Outlook cached mode is Enabled by default and OST file will be created?

    Yes, Cached Exchange mode is default when configuring Exchange account.

    Regards,

    Perry


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    • Marked as answer by Chomet Wednesday, August 21, 2019 5:26 AM
    Wednesday, August 21, 2019 1:32 AM
    Moderator

All replies

  • Hi Chomet,

    According to my research, Outlook has one Online mode but two offline modes: Exchange Cached mode and Offline Folders. Although Outlook doesn't use true offline folders, only cached mode, you need to disable offline folders along with cached mode to prevent it and older versions of Outlook from creating an OST file for offline use.

    We can disable offline use using group policy or by setting a registry value.

    • In the Group Policy editor, go to Microsoft Outlook > Account Settings > Exchange.
    • Set Do not allow an OST file to be created to Enable.
    • Click Cached Exchange mode folder.
    • Set Use Cached Exchange mode for new and existing Outlook profiles to disabled.

    These policies will set the following registry values

    HKEY_CURRENT_USER\Software\Policies\Microsoft\office\14.0\outlook\cached mode
    
    DWORD: enable
    
    Value: 0
    HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\OST
    
    DWORD: NoOST
    
    Value: 2

    NoOst value specifies whether or not an OST is created at startup. Setting the NoOst value to 2 will prevent the use of OST files. A value of 3 will allow OST files for cached mode but won't create one when online mode is used.

    Hope the information is helpful to you.

    Regards,

    Perry


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Tuesday, August 20, 2019 2:07 AM
    Moderator
  • Hi Perry,

    thanks for the info. I checked the computer running Outlook 2010.

    1. HKEY_CURRENT_USER\Software\Policies\Microsoft\office\15.0\outlook\cached mode

    > There is no Cached mode entry for \14.0\outlook

    2. HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\OST

    > There is no OST under \14.0\Outlook either.


    Tuesday, August 20, 2019 2:38 AM
  • Hi Chomet,

    Please manually create these keys if they don't exist.

    You can also install GPO templates and configure this via GPO.

    Office 2010 Administrative Template files (ADM, ADMX/ADML)

    Administrative Template files (ADMX/ADML) for Office 2016

    Please remember to wait few minutes and then restart Outlook to let policy take effect.

    Regards,

    Perry


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Tuesday, August 20, 2019 2:47 AM
    Moderator
  • Hi Perry,

    thanks.

    If the key does not exist, does that mean Outlook cached mode is Enabled by default and OST file will be created?

    Wednesday, August 21, 2019 1:11 AM
  • Hi Perry,

    thanks.

    If the key does not exist, does that mean Outlook cached mode is Enabled by default and OST file will be created?

    Yes, Cached Exchange mode is default when configuring Exchange account.

    Regards,

    Perry


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    • Marked as answer by Chomet Wednesday, August 21, 2019 5:26 AM
    Wednesday, August 21, 2019 1:32 AM
    Moderator
  • Hi thanks

    Is OST file created by default if the key does not exist too?

    The computers that runs Outlook 2010 and 2016 are in same OU.

    With cached mode not enabled, Outlook 2010 created a new OST file. but not the case for Outlook 2016 - no ost file created.

    Does the two version of Outlook behalf differently in term of OST creation by default?

    thanks

    Wednesday, August 21, 2019 6:37 AM
  • >>Is OST file created by default if the key does not exist too?

    Yes. Under Cached Exchange mode, .ost file will be created.

    >>Does the two version of Outlook behalf differently in term of OST creation by default?

    Theoretically, the behavior should be the same. I haven't seen official articles regarding this. I'm not sure what cause the difference. Maybe some windows-side aspect.

    Regards,

    Perry


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Wednesday, August 21, 2019 11:00 AM
    Moderator