Office 365: New port/URL required for OWA in Exchange Online
Below is a screenshot taken from Fiddler, when I open an OWA session against Exchange Online:
As you can see, besides port 443 against the misc. URLs, we now also establish a connection to "xsi.outlook.com" via port "10106".
This information is important for all customers, but especially for those that use OWA from the internal network (Kiosk users) and have configured client-side port restrictions.
The documentation will be updated with this information soon.