Outlook max PST and OST size

For Outlook 2016, 19, 21 and Microsoft 365

The default maximum size of a OST or PST is 50 GB. This is imposed by Microsoft because larger files are more difficult to manage and may be error prone.

The maximum size may be increased from 50GB by editing the Registry and entering two settings.

As usual, you should backup your registry before proceeding.

The following 2 new DWORD values must be created or set;

The default maximum size of a OST or PST is 50 GB. This is imposed by Microsoft because larger files are more difficult to manage and may be error prone.

The maximum size may be increased from 50GB by editing the Registry and entering two settings.

As usual, you should backup your registry before proceeding.

Load the Registry editor and go to;

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

If the PST folder is not present, you may create it.

The following 2 new DWORD values must be created or set;

WarnLargeFileSize
Don’t set this higher than 4090445042 (decimal) or f3cf3cf2 (hexadecimal)

MaxLargeFileSize
Don’t set this higher than 4294967295 (decimal) or ffffffff (hexadecimal)

The first value is how many MB a user can write to a pst-file or ost-file before receiving a warning that the file is full. The second value is how many MB the system can write to a pst-file or ost-file. This difference has to be at least 5%.

For a 100 MB – create/set a DWORD (32-bit) value to WarnLargeFileSize and enter the Decimal value of 95000. This value is 5% less than the MaxLargeFileSize.

Next create/set a DWORD (32-bit) value to MaxLargeFileSize and enter the Decimal value of 100000.

Next, enter the WarnLargeFileSize figure.

Next, enter the MaxLargeFileSize figure.

Exit the Registry editor and restart Outlook.