By default pst-file or ost-file size can grow as large as 20GB in Outlook 2007 & 50 GB in Outlook 2010, 2013, 2016, 2019 & office 365. If you configured Outlook to download shared folders, the content of shared folders will be stored in the local offline Outlook data (.ost) file. One way is to uncheck Download shared folders in the Cached Exchange Mode settings, in that case, your Shared Mailbox will be connecting directly to the Exchange Server. Or you can increase the .ost/.pst file size through the registry edit.
Make sure you backup from your Registry, serious problems might occur if you modify the registry incorrectly.
- Make sure Outlook is closed before doing the below steps
To increase the maximum size of PST & OST in Outlook, you will need to create a value (MaxLargeFileSize) in the following locations in the registry depending on what version of Outlook is being used.
1- Find the location in the Registry
2- Right-click and select DWORD (32-bit) Value. Then type MaxLargeFileSize
3- Double-click value & under Value data: add 11170 ( increase the .pst from 50GB to 70GB) then press OK.
4- Once you added the, your registry should look like this.
* use the below link for converting Decimal to Hexadecimal