Outlook Can Only Open 50GB PST File By Default

In order to modify registry entries, follow these steps:

1. Click Start, and then click Run, type Regedit, and then click OK.
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\PST (x.0 corresponds to the Outlook version: 16.0 = Outlook 2016, 15.0 = Outlook 2013, 14.0 = Outlook 2010)
3. Click PST, and then right-click MaxLargeFileSize in the right pane.
4. Click Modify, select Decimal and then type the limit (102400 for 100 GB) in the Value data
5. Click OK.
6. Right-click WarnLargeFileSize, and repeat steps 4 through 5 (if you set the value for MaxLargeSize to 100GB then set WarnLargeFileSize to 97280 - 95 GB).

Note: you may have to create the registry values if they do not exist. If the registry values do not exist, follow these steps to create them:

1. Click Start, click Run, type Regedit, and then click OK.
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook (x.0 corresponds to the Outlook version: 16.0 = Outlook 2016, 15.0 = Outlook 2013, 14.0 = Outlook 2010)
3. Right-click Outlook, point to New, and then click Key.
    

   

4. Type PST, and then press ENTER.
    

   

5. Right-click PST, point to New and then click DWORD
    

   

6. Type MaxLargeFileSize, and then press ENTER
7. In the Edit DWORD Value window, choose Decimal and type the limit in the Value data box, and then click OK.
    

   

8. Repeat steps 5 through 7 to create another DWORD WarnLargeFileSize, and then close the registry.

Value for registry entries should be set in either bytes or megabytes and you will need to calculate it first. You can use any online converter to calculate the value, for example this one - enter the gygabyte value, click Convert - the value you will need is the one in binary. The predefined values for 100 GB and 95 GB are as follows:

 MaxLargeFileSize for 100 GB = 102400 MB

 WarnLargeFileSize for 95 GB = 97280 MB

Notes:

• Despite the fact that you will be able to open .pst files that are larger than 50GB after making specified registry changes, it can still significantly decrease the performance of your Outlook application.
• We don't recommend increasing it to more than 100GB due to the nature of our shared environment.

In old Outlook data file types, the entries MaxFileSize and WarnFileSize were in use. Values under MaxFileSize and WarnFileSize have been used for the old-type ANSI format (an earlier Microsoft Outlook format) data files. The ANSI values are set in byte increments. Please note that since Outlook 2003 version the datafiles are in new UNICODE formats as ANSI format supports 2 GB data file maximum.

The MaxFileSize registry entry (default value is 2,075,149,312 bytes (1.933 GB)) 
The WarnFileSize registry entry  (default value is 1,950,368,768 bytes (1.816 GB))

If the old-type ANSI data file is in use please consider importing this .pst in the new profile. The old type data file has "Outlook Data File (97-2002)" in the format of the file. If the value of the MaxFileSize registry entry ever exceeds the ANSI 2 gigabyte (GB) limit on either the .pst or the .ost files, the value will be ignored to limit the size to 2 GB to prevent corruption.