[isodude]

The IDLE-command must be a push type of command? Which is used heavily by clients instead of polling.

As Microsoft does it with RPC is just a mess, they do a http call with 2billion bytes in request size, let the connection terminate at timeout and fire up a new call. I for one hope not that this is how JMAP solves it :(

[Mailtemi]

If submit an app to Apple with IDLE support I would bet will be rejected. JMAP has PushSubscription which will play nice with Apple / Google push services.

[heavenlyblue]

JMAP doesn't solve it at all.

[chrismorgan]

Sure it does. See https://jmap.io/#push-mechanism