Microsoft originally made EAS (Exchange ActiveSync) for mobile. All mobile device manufacturers support EAS and its not going anywhere. Its the perfect solution for mobile!
In Windows 10, Microsoft decided to offer EAS in the Windows Mail, Calendar and People applications and it works great. These were all built from the ground-up with EAS in mind!
Then, Microsoft decided to integrate EAS into Microsoft Outlook which was great because we could then prioritize an EAS implementation over MAPI and that would allow our customers to license ONLY ONE protocol which their users could use on both mobile and desktop! FYI, we pay Microsoft for every EAS license our customers use. When you buy our add-on a majority of that goes to Microsoft!
EAS has been available in Microsoft Outlook for almost 2 years. Microsoft has fixed most of the issues but because Microsoft Outlook is so legacy and really wasn't intended to work with a protocol like EAS, there are some cases, especially with REALLY LARGE mailboxes, where it could be a little problematic.
I personally use Microsoft Outlook 2016 with EAS on my 2 gigabyte mailbox. It works perfect. I also use EAS on my iPhone and Android phone. I also have Windows Mail connected via EAS. I then use Microsoft Outlook for Mac via EWS.
From time to time I use Mac Mail via EWS (Exchange Web Services) but Apple just blew up their Exchange integration with their most recent 10.13.2 release of MacOS. We have already contacted Apple and provided information to their engineers.
Soon, we will be offering MAPI which will be primarily for Microsoft Outlook users on Windows! This bugs me because now you need MAPI and EAS to provide full synchronization across desktop and mobile. But, this is what Microsoft wants and my guess is most of their decisions are for financial reasons!
Microsoft is even pulling functionality off Outlook.com and Google stopped supporting EAS on Gmail unless you are part of the G-suite. Google moved to use DAV for synchronization to avoid paying Microsoft.
Its all a nightmare and we're trying to make it as seamless and cost effective as possible for our customers!
Hope this helps, Tim