Outlook is a mail client for any email service you want to drop on there. It is part of Microsoft Office. Even though Exchange is going away, Outlook will still be there. If you use Outlook now, you can use it with your @maryviller2.com account - here are instructions on how to set that up:
The one confusing part is Outlook Web App (OWA) - what you use when you check your @maryville.k12.mo.us email online - is part of Exchange and will be going away.