Outlook has a default maximum size of 50 GB for modern PST files.
If a PST file reaches this limit, Outlook may stop receiving or moving email and display errors indicating that the Outlook data file has reached its maximum size.
The limit can be increased using the Windows Registry.
Close Outlook before making the change.
Press Windows Key + R, type regedit and press Enter.
Browse to:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST
If the PST key does not exist, right-click Outlook, select New > Key and name it:
PST
Right-click in the right-hand pane and create a new:
DWORD (32-bit) Value
Name it:
MaxLargeFileSize
Double-click it, select Decimal, and enter:
102400
This increases the maximum PST size to 100 GB.
Create another DWORD (32-bit) Value named:
WarnLargeFileSize
Set it to Decimal and enter:
97280
This sets the warning threshold to 95 GB.
Close Registry Editor and restart Outlook.
Important
The same settings also affect Outlook OST files.
Very large Outlook data files can reduce performance, so increasing the limit should not normally be used as a substitute for archiving or reducing the size of a mailbox.
The default 50 GB limit is generally preferable where possible.