Office 365: Selecting the Start Page (Outlook on the Web)
Microsoft has recently given users the choice of selecting which Web Application they wish to see as their Start Page when they log into their Office 365 account. This article describes how to set a start page for Office 365.
Continue by clicking the Gear symbol at the top right corner of the page to bring up the settings windows. Select the Start page option.
From the drop down menu, you are able to select which one of the Office Web applications you would like to start up when you login.
Click the Save button to confirm your selection.