Unknown process regularly updating unused outlook.pst file

Question

I have Microsoft Office 365 (Business) installed on my Windows 8.1 Pro machine. I have a .pst file from a previous job which I keep in case I need to revisit old emails. I (rarely) access this file using Outlook. On the same machine I have Dropbox installed and I keep all my personal files synced online.

Periodically, perhaps once every few hours if I'm paying attention, and often when Windows starts up I see that Dropbox is syncing something. When I click on the icon in System Tray it says it's syncing Outlook.pst and that the file is currently locked.

The problems are 1) there's no reason for that file to be changing when I'm not using it and 2) I don't know of anything that should be reading it.

I don't have Outlook configured to start automatically anywhere. I have configured Windows Search to not index .pst files. However the last modified date on the .pst is regularly changing.

If I change the name of the file I get a prompt on startup, after standby, and periodically during normal operation saying "The file C:\Users...Outlook.pst cannot be found". Clicking OK brings up an Open File dialog to locate or create the .pst. Task Manager shows Outlook running with only around 10MB memory.

I believe OneDrive for Business came packaged with Office 365 but I've done my best to disable that anywhere I can find it.

Any suggestions on how I remove this irritation and prevent anything from accessing & updating outlook.pst would be very welcome.

Answer 1

Here are some tools that will help find out what is happening.

Process Explorer

Use it to find with certainty which program is looking for the Outlook.pst file.

Rename the file, and when the dialog appears, start Process Explorer, then drag the icon on top of the message. Process Explorer will then indicate which program owns that dialog.

Autoruns for Windows

Use this to find out how this program starts up with Windows. Start Autoruns, wait for the load to be finished, then click the Find button (or Ctrl-F) and search for that program. If you want to stop it from starting with the computer, uncheck its checkbox. Autoruns will still remember it and you can always undo that action by restoring the check-mark.

Process Monitor

If you are still unsure which product is touching the Outlook.pst file, use Process Monitor to trace all activity on the file.

Start Process Monitor up and a filter dialog will appear. Uncheck all the default filters, and create a new filter as below and click Add and OK. Leave the Process Monitor running with this filter until it finds the process that touches the file.

Answer 2

Skype for Business (formerly known as Lync) pokes around in local PST files.

I believe that if you disable the saving of conversations it will stop writing but I am not in a position to be able to try that.

Answer 3

The frequent cause is OneNote from Microsoft Office suite. If you use the following Outlook Tasks command:

then Outlook.exe gets started. Some other OneNote commands which use Outlook functionality can be causing this, too.