Is this a duplicate pst?

[LaPlume]

New Windows 11 computer; Outlook 2021; all accounts are POP3.

I copied the pst file from my old PC (Outlook 2010) and imported it into the new Outlook. Everything is working well.

The pst I’m using is named Outlook.pst and is about 1,905,000 KB. But there’s another pst in the same folder whose name is one of my email addresses. It's only 265 KB. I opened it and was surprised that it appears to be a duplicate of the file I’m using – same folder structure, same messages, same address book. But if it’s the same data, how can its size be so much smaller? Opening it took a couple seconds, whereas reopening the larger file took over a minute.

If I delete the small file, will that have any impact on the much larger one?

Thanks.