This post describes a nasty privacy issue with Outlook:
https://tuta.com/blog/outlook-business-security-issue
It's complicated so I'll summarize the actions that I see. I'm assuming here that you don't want all your email credentials stored in the Microsoft cloud.
1. Hopefully you're still using "Outlook (classic)" (good) instead of "Outlook for Windows" (bad).
Classic Outlook comes from a Microsoft 365 download while Outlook for Windows is either built into Windows or comes from the Microsoft Store.
To figure out: press the Windows key then type: outlook
You're good if you see this, viz. "Outlook (classic)":
2. Hopefully you're still on the "old" Outlook (good), i.e., you haven't yet moved to the New Outlook (bad).
In Classic Outlook, Microsoft added a toggle in the top right corner to try to encourage you to switch:
You're good if you see this, viz. "Off":
3. Assuming you're still using Classic Outlook with the New Outlook toggle "off", hide the toggle so that you don't turn it on by mistake. To do this, add two values in the registry using regedit:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\General
Add DWORD: HideNewOutlookToggle, value= 1
HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\Options\General
Add DWORD: HideNewOutlookToggle, value= 1
(You might need to add the keys "Options" then "General" before you can add the DWORD.)
