Paul, Neal,
This functionality was fixed in SmarterMail 15.0.5962 (Apr 28, 2016)
Fixed: Exchange Web Services now implements streaming events that push changes from the server to the client.
I've confirmed that my email updates are pushed to my 15.7.6837 EWS account that's set up in Apple Mail on High Sierra.
Andrea Free
SmarterTools Inc.
877-357-6278
www.smartertools.com