Beginning with Outlook 2003, the new Unicode pst/ost format support much larger data files, with the default data file size set to 20 GB (Outlook 2003 or 2007) and 50 GB for Outlook 2010 and up. While this size is more than enough for most people, it can be raised in Outlook 2003/2007, if needed, by setting two registry values. The default file size in Outlook 2010 and up of 50GB is currently the maximum recommended limit for all versions of Outlook. (You can raise it to 100GB if necessary, but it is not recommended.)
Note: At this time, the maximum recommended ost or pst file size is 50GB.
Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST (replacing xx with your version of Outlook: 16 for Outlook 2016, 15 for Outlook 2013, 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.)
Unicode pst format
For Unicode pst and ost files, create DWORD values of
MaxLargeFileSize
WarnLargeFileSize
Enter a decimal value in MB. For example, 100 GB = 102400 Decimal (a GB to MB or bytes converter is below). Maximum Unicode pst/ost file size is 1TB or 1024 GB.
For ANSI format pst file, you need to create DWORD values named
MaxFileSize
WarnFileSize
Enter a decimal value in Bytes. For example, 1 GB = 1073741824 Decimal (a MB or bytes converter is below). Note that the maximum file size for ANSI pst is 1.9 GB.
Administrators can control it using group policy by editing the following key.
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\PST
As always, replace xx with your version of Outlook: 16 for Outlook 2016, 15 for Outlook 2013, 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.
MaxLargeFileSize – this value sets the maximum size of a Unicode pst or ost. In Outlook 2010 and Outlook 2013, the default is 50 GB; in Outlook 2003 and 2007, it’s 20 GB. Value range (in Hex) is 0x00000001 – 0x0000C800; when entering the value in Decimal, use MB.
WarnLargeFileSize – this value sets the warning level used with Unicode pst/ost files, so you know when the pst or ost is too large. The recommended warning is at 95% of the data file size. When entering the value in Decimal, use MB.
ANSI pst format
MaxFileSize – this value sets the maximum file size for ANSI format pst files. The default is 1.933 GB (2075149312 bytes), with the maximum allowed value of 1.9375 GB (2080392192 bytes). Value range (in Hex) is 0x001F4400 – 0x7C004400. When entering the value in Decimal, use bytes.
WarnFileSize – this value set the warning limit for ANSI format pst files. The default is to warn when the pst reaches 1.816 GB (1950368768 bytes) Value range is 0x00042400 – 0x7C004400. When entering the value in Decimal, use bytes.
Actively using an ANSI pst in Outlook 2016 is not recommended. Import the pst into a new Unicode pst if you need to keep an older PST in Outlook.
Registry Paths
Enter the values under the appropriate key for your version of Outlook:
Outlook 2016:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST
Outlook 2013:
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST
Outlook 2010:
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST
Outlook 2007:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST
Outlook 2003:
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST
Administrators will set these values using group policy:
Outlook 2016:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PST
Outlook 2013:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\PST
Outlook 2010:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\PST
Outlook 2007:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\PST
Outlook 2003:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\PST
Restore Default Values
To revert to the defaults, if the pst is larger than the default size, shrink the pst or ost so that its well below 20 GB (Outlook 2003/2007) or 50 GB (Outlook 2010/2013/2016) or below 1.8 GB for ANSI format, then delete the appropriate MAX* and WARN* registry keys for the pst format.
Restart Outlook for the changes to take effect.