When you log into your 365 email account it is defaulted to show your emails in 'conversation view'.

At the top of the message pane, click on CONVERSATIONS BY DATE to see the drop down menu of options (see screenshots - click on them to see full size version).

Go to the end of the list to see the conversations section and ensure the tick is alongside off to turn it off.

The SORT BY and ORDER options are relevant to messages whether you have the messages shown in conversation view or not.