changee size ost file

Question

I use mapi protocol

outlook 2021

exchange 2019 cu13

How can I change the size of the .ost file

Currently the maximum is 50 GB

Answer 1

Hi,

Welcome to Microsoft Q&A community!

To increase the size of your .ost file in Outlook 2021 with Exchange 2019 CU13, you’ll need to modify the Windows Registry. Here are the steps:

Open the Registry Editor:

• Press Windows + R to open the Run dialog box.
  • Type regedit and press Enter.

1. Navigate to the appropriate registry path:
   • For Outlook 2021, go to:HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

Modify or create the necessary registry entries:

• MaxLargeFileSize: This entry sets the maximum size of the .ost file. You can set this value up to 4096 GB (4 TB), but it’s practical to set it to a reasonable size like 100 GB.
• WarnLargeFileSize: This entry sets the warning size for the .ost file. Typically, this should be slightly less than the MaxLargeFileSize.

To create or modify these entries:

  - Right-click on the right pane, select **`New > DWORD (32-bit) Value`**.
  
     - Name the new value **`MaxLargeFileSize`**.
     
        - Double-click on it and set the value in MB (for example, 102400 for 100 GB).
        
           - Repeat the steps to create **`WarnLargeFileSize`** and set it to a value slightly less than **`MaxLargeFileSize`** (e.g., 97280 for 95 GB).
           
           **Restart Outlook**:
           
              - Close and reopen Outlook for the changes to take effect.
              

Here’s a quick summary of the registry entries:

• MaxLargeFileSize: Set to your desired maximum size in MB.
• WarnLargeFileSize: Set to a value slightly less than MaxLargeFileSize in MB.

More details you can refer to:https://support.microsoft.com/en-us/topic/how-to-configure-the-size-limit-for-both-pst-and-ost-files-in-outlook-2f13f558-d40e-9c2a-e3b6-02806fa535f4