We've reviewed the traffic from the Zoom client when trying to synchronize data with EWS. Calendars is pretty straightforward - it simply asks for the items in the default calendar folder.
However, when the Zoom client tries to sync contacts, it does so in a less direct manner. It first asks for folders that are in the default contact folder, using the returned data to determine the specific ID of the default contact folder. The client then uses the identified ID to ask for the actual contacts in that folder. This approach works with Exchange since Exchange has all sorts of hidden folders, so it has data to return when asked for folders in the default contact folder. SmarterMail does not have a similar structure, so it has nothing to return at that stage, so the Zoom client simply gives up.
This corresponds to what @Michael relayed from his conversation with Zoom - we are returning zero results in response to a request for folders contained in the default contact folder. The Zoom client is not asking the SmarterMail server to retrieve any contacts.
Instead of trying to go back and forth with Zoom, we have opted to implement a workaround in SmarterMail that will return some data when Zoom asks for folders in the default contact folder.
Andrew Barker
Software Developer
SmarterTools Inc.
(877) 357-6278
www.smartertools.com