Using New Outlook on Windows for personal email, calendar, and contact management
You can stop messages from being sent to the Archive folder by avoiding the Backspace key, which archives items in classic Outlook. Instead, use the Delete key or the Delete/trash button.
Also, check the Outlook mobile app's Swipe Actions settings to make sure swiping isn't configured to archive messages. In classic Outlook, go to File > Manage Rules & Alerts and check that no rule is automatically moving messages to the Archive folder.
If you want to disable automatic archiving, go to File > Options > Advanced > AutoArchive Settings and clear Run AutoArchive every n days. This prevents Outlook from automatically running AutoArchive.
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hth
Marcin