Outlook 2016 other calendars not updating
Much development effort is going into those APIs to make sure that all of the scenarios considered by the Outlook team are available, so the decision was made to use the REST-based APIs to communicate with Exchange Online and other Office 365 components.
The next big issue that had to be solved was how to deal with the proprietary API calls used by the Outlook clients to communicate with the back end.
Enough information is synchronized initially to make the mailbox usable for the Outlook app and eventually the complete contents of the mailbox will be synchronized.
Figure 1: The Outlook app architecture for communicating with Office 365 (Image Credit: Microsoft) One restriction that is introduced is that an Outlook client can only connect to a single Office 365 region at a time. government Office 365 regions will be unable to use the Outlook apps until Microsoft deploys the necessary infrastructure with a specific dependency being the availability of the Azure protocol translator in those regions.
This means that you can’t setup a client to connect to a mailbox belonging to an Office 365 tenant in the U. and another belonging to an Office 365 tenant in Europe. The new architecture is simple and elegant when it comes to Office 365, but Outlook mobile clients are also used with many on-premises mailboxes.
Making a quick move to Azure is all very well, but the problems involved in transforming an architecture that has to function at the scale of Office 365 is a tad more complicated than simply moving data from one cloud service to another.
Small items like data sovereignty (where data is stored) have to be taken into account, as must the distributed nature of Office 365, which currently operates over twelve datacenter regions distributed around the world.