For reasons too long and irrelevant to get into, I had to suddenly reformat my computer because of a Windows OS crash and then reinstall Outlook 365.



While trying to merge data from old Outlook files into the new Outlook file (to capture old emails I had lost in my crash), I noticed that when I closed Outlook and went to Windows Explorer to manage the file, the size of the default Outlook.pst file keep decreasing, even thought the active process was closed.

I took a Snagit video too big to post here, but it can be seen at this link:

https://drive.google.com/open?id=1CZ...3c6aWIM-DXJvlB

It finally ended up at about 918MB, more than half a gig less than what you see in this video.

I had never seen anything like this before. Can somebody explain what's going on here? Is the file being compacted? Is it archiving old emails in the background? I can;t make heads or tails out of this. Can anyone help?

Probably because Outlook was compressing the data file in the background - a process that will continue after you exit Outlook.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

OK, thanks for the insight.