I have been using Outlook for the last few months, and my PST file has grown to about 12 GB. Outlook has become slow, and the system is also getting affected. After a lot of searching on the Internet, I found Softaken Compress PST Software. I used its free trial version and the result was quite good. This tool:
Compresses large PST files quickly and safely
Saves space by separating attachments
Compatible with any version of Outlook
Compresses the file without data loss

Read More:- https://www.softaken.com/compress-pst-pro

I have been using Outlook for a long time and the size of my PST file has gone up to more than 10GB. This has slowed down Outlook's speed. Even after deleting, the size was not reducing. Then I used DataVare Outlook PST Compact Expert tool and the result was quite good. This tool reduces the size of the PST file without any data loss, and also gives the option to save attachments separately. The interface of the software is quite simple, and you can compact multiple files at once. Those who find Outlook slow or the PST size has increased a lot, must try it once.

Read More:- https://www.datavare.com/software/outlook-pst-compact-expert.html

To manually compress a PST file, open Outlook, go to File > Account Settings, select the PST file, and click Compact Now. However, this method is slow, often ineffective for large files, and may not significantly reduce size. For a more efficient solution, consider using DRS Softech PST Compress Tool, which quickly shrinks PST files without data loss and handles large files seamlessly.

Read More: https://www.drssoftech.com/pst-compress/