I was able to do this using OWA access and as long as I was logged into the web portal my sharepoint would show my calendar. I would assume you could do this with Inbox as well but have not played with this yet. When I do I will post here.
When I am not connected to my portal the window where my calendar shows my logon location for my mail server and when I type in my credentials I am in.
using
HTTPS://mail.domainname/exchange/By the way my sharepoint is out of my domain and there is no connection to my internal domain servers so I have to use OWA