How can I mount a data file (pst) in new outlook. In the classic version this is doable through the File menu which is not available in new outlook.

You have to change to "old outlook". If it's not loaded on your system, hopefully you can download it from microsoft. "new outlook" deleted my old outlook file (with no notification) when I selected it so I had to download it. At the time the "revert to old" button did not work. I don't know if they've fixed that. Please complain to microsoft - maybe if enough of us do they will reconsider.

To everyone who said to go back to the old outlook... I'm here because my old outlook was very old. microsoft decided to force 2 factor on everyone's account, but the old outlook i used really doesn't work with 2fa. I spent hours creating and recreating static application passwords in the 2fa security page for a year before it stopped working altogether.

i am a fan of 2fa and use it everywhere. But microsoft needs to support basic features in current products if they are going to herd everyone to them.

I came to this thread because of THIS specific comment. I have a discovery search export that I cannot open. Did you make any progress on viewing the content?

Adding an update on this thread from my comment many months ago.

Wanted to clarify for folks that when there is a reference to the "old" Outlook, this doesn't have to be a significantly older major version - perhaps the more applicable term would be "Classic Outlook".

For those who are M365 users, this is what I've found userful for myself, and also in deploying new endpoints to our team members:

1. Download & install the desktop applications of Outlook on the (new) device.
2. If you're a M365 subscriber, you should be able to do this by going to "office.com", make sure you're logged in, and from there you should see a button on the right side of the page below the "Microsoft 365" banner that says "Install and more". From there, you can download the apps - once downloaded, install. (Screenshot below)
3. After installed, open Outlook. As of last week when I deployed four new endpoints, it's going to default to the "new" Outlook. But from within the application, you can go to "Help" in the top bar, and from there you should see an option to click to switch to "Classic Outlook".
4. To make things clear for my endpoint users, after it opens the "Classic" Outlook, I immediately pin it to the Taskbar, (and unpin the "New Outlook" if it was there), that way the users are clicking to open THAT version every time.
5. Within the Classic version you can import your classic .pst files, and create new ones as needed.

Hope this helps folks! (And I hope this work-around remains viable without any further forced application updates from MS).

Nobody's asking again for Classic. That's already been discussed above. What's still needed is for MS to fix their ignorant decision and support pst files in the new Outlook.