Got the same problem with MacMail, was using CardDAV, which no longer works with latest IOS, we then added EWS. And tried to setup syncing contacts and calendars as Exchange, but whenever exchange account is created keeps on saying it's "offline".
Therefore now cannot sync contacts & calendars with either CardDAV or EWS. Before the IOS update on the Mac laptop, contacts & calendar syncing was working perfectly fine, and there was no need for EWS.
Interestingly on iPhone and iPad works fine.
Already opened support ticket and we've been testing back and forth since November/December!
Really hope smartermail put extra effort / resources to resolve this issue asap.