in response to neil hedley with subtasks in outlook

an easy way to do this is to create a custom column in outlook called
project

then assign a project for each todo

if you group by project in a todo list then each project will have all it's related tasks in a "project" like format wiuth each task made out like a subtask-- outlined and suboutlined

might not be exactly as desired but goes a long way toward getting both vertical and horizontal view of your actions/project