How to increase the maximum size for PST-files and OST- files in Outlook

The size of the file remains always in the centre of the process, so, the Concern about the size of the OST-files and PST- files is obvious. As we know, the maximum recommended size of PST-file and OST-file (Unicode) in Outlook 2003 and 2007 was limited to 20 GB. And in Outlook 2010, 2013 and 2016, the maximum limit increased to 50 GB. But sometimes due to ignorance of oversized OST files, the working process gets inversely affected and file may get corrupted; at that time by going through this way, the user can get rid of this.

For the better understanding of configurations of Outlook versions; details are given below:

For Outlook 2019, 2016, 2013 and 2010

For Outlook 2007 and Outlook 2003

As default size for the PST-files and OST-files is 50 GB and users wish to maximise the size. It can be done by the Registry value, itallows to maximise the size up to approx. 4PB (4096 TB). But the main question is…

How to increase the maximum size limit?

Via the Registrythe size of files can be modified i.e. increase or decrease. But this method doesn’t apply on the Outlook 97-2002 format’s OST and PST files. I.e. PST files of ANSI format.

Via the Registry

For the increase in the maximum size of Outlook’s PST-files and OST-files, the user has to create and set 2 values in the given location in the Registry:

• For Outlook 2003

  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\11.0\Outlook\PST

• For Outlook 2007

  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\12.0\Outlook\PST

• For Outlook 2010

  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\14.0\Outlook\PST

• For Outlook 2013

  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\15.0\Outlook\PST

• For Outlook 2016

  HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\PST

  NOTE: The steps that are given above; applies to both PST and OST files.

  For the successful implementation of the process; the given DWORD values create or set for Non-Unicode PST/OST files:

• MaxFileSize
• WarnFileSize

To execute the process successfully; the following 2 new DWORD values create or set for UNICODE PST/OST files

• WarnLargeFileSize
• MaxLargeFileSize



The first value (WarnLargeFileSize) indicates that before getting the warning of full file how many MB a user can write to a PST-file or OST-file. The second value (MaxLargeFileSize) is the measure of MB the system can write to a PST-File or OST-File.It is to be noticed that for the best practice and genuine working; the difference between Warn Large File Size and Max Large File Size should be at least 5%. In case due to the oversize of files, if the corruption of PST files takes place, this is how you can repair and recover the corrupted PST files.

Here, in this example, the maximum size of PST-files and OST-files has been set to 105 GB with the warning at 98 GB.

For the increase in the maximum size of Outlook’s PST-files and OST-files, the user has to create and set 2 values in the given location in the Registry:

What other options users have?

To increase the maximum size for PST and OST, the above-described method is the best way but if your focus concern is oversized files which can inversely affect working or may lead to corruption; you also have the option to split or compress PST. Using Professionals way users can split PST Files as per their need and can also compress PST Files and can reduce its size without any concern and can get proficiently rid of oversized PST. Shoviv PST Management Suite is a multipurpose all-in-one software for PST that expertly handles all the tasks of PST. Download it and try its free trial/demo version to see its working.