You can manually reduce the size by deleting unnecessary emails and attachments, archiving older data, or using Outlook’s Compact Now option. But these methods may not be suitable if you need to keep all your emails.

In that case, SysTools PST Splitter is a practical option. It can split a large Outlook PST into smaller files based on size, date, folder, or other criteria, while keeping the existing mailbox data intact.

If your PST has become too large, splitting it into smaller files can make it easier to manage and work with in Outlook. Always keep a backup of the original PST before making any changes.