I believe you'll have to be more specific about what's actually happening (which clearly you don't want) and what you'd like to be happening instead. It would also help to know how you have Outlook set up as far as conversation view goes and/or whether your various e-mail lists have their respective messages filtered into folders other than inbox, and whether you're viewing from those folders.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore