Comment by Mailtemi

As a JMAP client implementer, there’s a big plus, beside JMAP, in having an integrated server for email, contacts, and files. Some setups take days even for email, so an easy, fast setup saves a lot of time.

Also, after code the CalDAV ↔ JSCalendar part, using only IANA time zones instead of scattered ones in CalDAV components makes things much simpler.