You cannot start Outlook in cached mode or create a new cached mode profile

Á við um: Outlook 2019Outlook 2016Outlook 2013


When you start Microsoft Outlook in cached mode, you receive the following error message:

Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. There is not enough memory available to perform the operation.

Note This error message is also displayed when you try to create a new Outlook profile that is configured to use cached mode.


This problem occurs because the hidden PR_OST_OSTID property in your mailbox is larger than 32 kilobytes (KB).

This property is located on Top of Information Store in the default store. Every time that you create a new cached mode profile for the mailbox, approximately 20 bytes of data is added to this property. Eventually, the size of the data in the property exceeds approximately 32,720 bytes, and you start to receive the error.


To resolve this problem, remove the data in the PR_OST_OSTID binary property. To do this, follow these steps:
  1. Download and extract the MFCMAPI tool from
  2. Launch Mfcmapi.exe, and then click OK to move through the introduction screen.
  3. On the Tools menu, click Options.
  4. Enable the following options, and then click OK:
    • Use the MDB_ONLINE flag when calling OpenMsgStore
    • Use the MAPI_NO_CACHE flag when calling OpenEntry

  5. On the Session menu, click Logon.
  6. Select the Outlook cached mode profile for the mailbox, and then click OK.
  7. Double-click the email address that represents the mailbox in question.
  8. In the navigation pane, expand Root Container, and then select Top of Information Store.
  9. In the right-side pane, locate the PR_OST_OSTID property.

    Note You may see PR_OST_OSTID under the Property names column or the Other names column. If it is found under the Property names column, the value under the Tag column is 0x7C040102. If PR_OST_OSTID is found under the Other names column, the value under the Tag column is 0x7C04000A.
    1. If the value under the Tag column is 0x7C040102, then double-click PR_OST_OSTID to open the Property Editor.
    2. If the value under the Tag column is 0x7C04000A, then right-click PR_OST_OSTID, click Edit as stream, and then click Binary.

  10. Right-click the data in the Binary section of Property Editor, and then click Select All.

  11. Right-click the selected data in the Binary section, and then click Delete.
  12. Click OK.
  13. Exit the MFCMAPI tool, and then start Outlook.

More Information

There are several scenarios in which this situation might occur:   
  1. Many users log on to the mailbox repeatedly. (For example, many users log on to a mailbox that is used to answer public or service communications.)
  2. Many users open a shared resource mailbox when Download shared folders is enabled in the Outlook profile.
  3. Someone is creating new cached mode profiles for their mailbox repeatedly. (This occurs only rarely.)