Are you talking about 'Threading' ? Select Inbox View > Sort by > Select 'Unthreaded'

Then set this up on all folders Right click on the column headers to see drop down At bottom select 'Apply current view to'....choose 'folder and it's children' choose the account name and then the account name.

You can also check the following is selected : Menu icon > Settings > General Scroll to bottom and click on 'Config Editor' You may get a friendly warning :) In top search type: view_flags look for : mailnews.default_view_flags If set to 1: click on the pencil icon on the right to edit Remove the number 1 and type number: 0 click on the tick icon to save

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