Well to be honest, EWS is quite good protocol, much better than IMAP, only Kerio implementation of EWS is very bad. The reason why MS is discontinuing EWS is completely different (basically to get rid of third parties and limit functionality for external tools). We’ve reported a lot of bugs to Kerio in their EWS implementation, but they have never fixed anything. Their EWS implementation was meant only for Outlook for Mac and it was very limited. Communication with Kerio is generally very complicated. There are server providers that listen and are willing to fix the bugs and there are some that are not.