If you have enabled the ‘Flagged email’ option from settings in To Do, then any email you flag in Outlook will show up under the ‘Flagged email’ smartlist.
From the Outlook web app, you can create a task out of an email by right-clicking —> Advanced actions —> Create task. You can also select a message in the body of an email and create a task out of it.
An error occurred while saving the commentTom S commented
I use an installed version of 365. when I click an email in to do, it opens it under the web version of office, which I normally don't use. Can this be changed?