Using classic Outlook for Windows in business environments
Are you using the "backspace" key to delete the email? Unfortunately, said key is hard-mapped to "archive" the item instead, that is move it to the Archive folder. You can use the Delete key instead.
If you feel comfortable working with the registry, you can also disable the "hit Backspace to archive items" behavior, as explained for example here: https://office365itpros.com/2022/09/02/outlook-archive-folder/