This article applies only to Outlook for Windows.

By default Outlook desktop application is able to open .pst files and create .ost which size is not more than 50 GB. If you try to open .pst file which is more than 50 GB in size, you will receive the following error:

Error

In order to increase maximum size of the .pst and .ost files that your Outlook can open or create you will need to add or modify following registry entries:

  • The MaxFileSize registry entry (default value is 2,075,149,312 bytes (1.933 GB)) 
  • The WarnFileSize registry entry  (default value is 1,950,368,768 bytes (1.816 GB))
  • The MaxLargeFileSize registry entry (default value is 51,200 MB (50 GB)) 
  • The WarnLargeFileSize registry entry (default value is 48,640 MB (47.5 GB))

The MaxLargeFileSize registry entry and the WarnLargeFileSize registry entry refer to a UNICODE formatted (new Large format) file, and the MaxFileSize registry entry and the WarnFileSize registry entry refer to an ANSI formatted (an earlier Microsoft Outlook format) file. The UNICODE values are set in megabyte (MB) increments, while the ANSI values are set in byte increments.

The MaxFileSize and MaxLargeFileSize determine the absolute maximum size that both the .pst and the .ost files can grow to. After this maximum size is reached, Outlook does not permit the size of the file to grow beyond this size.

The WarnFileSize and WarnLargeFileSize determines the maximum data that both the .pst and the .ost files can have. After this maximum data is reached, neither the .pst nor the .ost files are permitted to add any more data. However, the size of the physical file may still increase because of internal processes.

Important: it is recommended that the values between the MaxFileSize registry entry and the WarnFileSize registry entry, and the values between the MaxLargeFileSize registry entry and the WarnLargeFileSize registry entry be at least 5 percent (%) so that internal processes are not hindered from continuing.

These settings apply to both .ost and .pst files. If you modify these registry values, this can affect .ost files that are used with Cached Exchange Mode, with AutoArchive, and with .pst. files. If Outlook is configured to download shared folders, the contents of shared folders are stored in the local Offline Outlook Data (.ost) file. If the shared folders contain many items or large attachments, the size of the .ost file may grow significantly.

In order to modify registry entries, follow these steps:

  1. Click Start, and then click Run, type Regedit, and then click OK.
  2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\PST (x.0 corresponds to the Outlook version: 16.0 = Outlook 2016, 15.0 = Outlook 2013, 14.0 = Outlook 2010)
  3. Click PST, and then right-click MaxFileSize in the right pane.
  4. Click Modify, and then type the value in the Value data
  5. Click OK.
  6. Right-click WarnFileSize, and repeat steps 4 through 5.
  7. Right-click MaxLargeFileSize, and repeat steps 4 through 5.
  8. Right-click WarnLargeFileSize, and repeat steps 4 through 5.

Note: you may have to create the registry values if they do not exist. If the registry values do not exist, follow these steps to create them:

  1. Click Start, click Run, type Regedit, and then click OK.
  2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook (x.0 corresponds to the Outlook version: 16.0 = Outlook 2016, 15.0 = Outlook 2013, 14.0 = Outlook 2010)
  3. Right click Outlook, point to New, and then click Key.
    PST
  4. Type PST, and then press ENTER.
    PST 2
  5. Right click PST, point to New, and then click DWORD
    DWORD
  6. Type MaxFileSize, and then press ENTER
  7. In the Edit DWORD Value window, choose Decimal and type the value in the Value data box, and then click OK.
    Value
  8. Repeat steps 5 through 7 to create another DWORD WarnFileSize.
  9. Repeat steps 5 through 7 to create another DWORD MaxLargeFileSize.
  10. Repeat steps 5 through 7 to create another DWORD WarnLargeFileSize, and then close the registry.

Value for registry entries should be set in either bytes or megabytes and you will need to calculate it first. You can find predefined values for 100 GB and 95 GB below:

MaxFileSize and MaxLargeFileSize should be 100 GB = 102400 MB = 107374182400 bytes 

WarnFileSize and WarnLargeFileSize should be 95 GB = 97280 MB = 102005473280 bytes 

Important: value of WarnFileSize and MaxFileSize should be set in bytes. Value of MaxLargeFileSize and WarnLargeFileSize should be set in MB's.

Notes:

  • Despite the fact that you will be able to open .pst files that are larger than 50GB after making specified registry changes, it can still significantly decrease performance of your Outlook application.
  • We don't recommend to increase it more than 100GB due to the nature of our shared environment.