Outlook pst file is too huge with POP3. How to save more space?

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Outlook version
Outlook 2016 64 bit
Email Account
My outlook pst file has reached 39GB and is still growing. I am using POP3 connection.

I've Google around and I found sites suggesting to "Compact now" to shrink the size. I have many important email and attachments and I don't want to risk my mailbox for that unless this feature is proven to shrink more than 50% of the original pst file size.

Other than that, if I use outlook archive feature, it will still create another file with different extension but will consume the same space as before right?
For example:
originally - 39GB .pst
after archive - 15GB .ost and 14.pst (totalling 39GB)

What else can I do to save space?
According to my view, you can use third-party software to split the large PST file.
Compact now will not delete mail - it removes white space, left from messages you deleted. At 39 GB, I would not be surprised to see it drop to about 30 GB.

A pst file is a database. When you empty deleted items, it removes the message from the database index but the message data remains. This remainder is 'white space' When the computer is idle and there is more than 20% of white space, outlook will compact it, a few bits at a time. The problem is that when the pst is huge, 20% is a lot... If you close outlook or turn the computer off, you won't have idle time.

If you need to reduce it more, rather than using a commercial pst splitter, archive the older mail to a new pst. But - depending on how much mail you get and keep, 20GB might keep you for a long time.
I have used Outlook many years and continue with the POP3 approach. I have overcome the size issue purely by utilising the AutoArchive functionality that has been available in each version. I set it up such that the default is to archive emails older than 3 months into Archive9999.pst where 9999 is the current year. On 1st April each year I create a new empty pst file and change the default to that - so, for example, on 1st April 2021 I will change the default archive file name from Archive2020.pst to Archive2021.pst . This keeps the "current" file to a reasonable size (for backup purposes), while maintaining a manageable archive (my archive files go back to pre-2006 with a total size of over 500mb), and "yes" I do occasionally go back to emails in those earlier files!
What do you consider a reasonable size for backup? The default max pst size is 50 GB for new versions, 20 GB for older versions. While I don't consider 20 GB to be reasonable for backing up (let alone 50), 500 MB is a bit small... I'd go with under 5 GB for speed and manageability, up to 10 GB to avoid too many pst files.

Because having a ton of pst files (20+ going back to the early days of email) open can be as hard to manage as a single large pst - and they need to be open to search, unless you use a 3rd party search utility. Or only open the pst when you need something - but then you need to know the year.
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