Microsoft quietly added the ability to schedule emails on Outlook.com without telling anyone. Users can now easily do it from the web interface. The feature allows users to schedule an email for a later date from Outlook on the Web. Email composition can now be sent immediately or discarded from the Drafts folder. The email will now sit in the drafts folder until it is ready to be sent. To change or cancel a scheduled email, click on the ‘Cancel Send’ button to cancel the email.
Source: https://www.bleepingcomputer.com/news/microsoft/outlookcom-now-lets-you-schedule-emails-for-a-later-date/