OST File Size Limit

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How to configure OST file size limit?

You can configure OST file size limit as required using Outlook registries. MS Office Outlook versions 2013, 2010, 2007 and 2003 support American National Standards Institute (ANSI) and UNICODE personal folders (.pst) and offline folder (.ost) files. So you can configure size limit for both OST and PST files. The following entries help you in doing so.

  • MaxFileSize registry entry - It determines the absolute maximum size that OST file can grow to. After this maximum size is reached, Outlook does not permit the size of the file to grow beyond this size limit.
  • WarnFileSize registry entry - It determines the maximum data that OST file can contain. After this maximum data is reached, OST file is not permitted to add any more data.
Location for these registry entries is located in following path in Registry Editor:

Outlook 2010 » HKEY_CURRENT_USER\ Software\ Microsoft\ Office\ 14.0\ Outlook\ OST

Outlook 2007 » HKEY_CURRENT_USER\ Software\ Microsoft\ Office\ 12.0\ Outlook\ OST

Outlook 2003 » HKEY_CURRENT_USER\ Software\ Microsoft\ Office\ 11.0\ Outlook\ OST

Now, follow the given below steps to configure the size limit for the OST file.

  1. Click Start, and then click Run.
  2. Type Regedit, and then click OK.
  3. In the left pane, expand My Computer, and then expand HKEY_CURRENT_USER.
  4. Expand Software, and then expand Microsoft, and then expand Office.
  5. Expand 11.0 for Outlook 2003, 12.0 for Outlook 2007, or 14.0 for Outlook 2010, and then expand Outlook.
  6. Click OST, and then right-click MaxFileSize in the right pane.
  7. Click Modify, and then type the value in the Value data box.
  8. Click OK.
  9. Right-click WarnFileSize, and repeat steps 7 through 8.
  10. Right-click MaxLargeFileSize, and repeat steps 7 through 8.
  11. Right-click WarnLargeFileSize, and repeat steps 7 through 8.


This way user can configure OST file size limit easily in MS Outlook 2013, 2010, 2007 or 2003. It is to be noted that if OST file reaches the limit that is specified in the WarnFileSize or the WarnLargeFileSize registries, the compaction function is automatically triggered to try to reduce the size of the file to a usable level.