Hmm. I'm a happy FastMail customer of >2 years, but sometimes the web app loses the connection with the host (especially when on flaky wifi) and fails to re-establish it. This is really aggrevating when you hit send on an email, which disables the input text box but then just hangs indefinitely in a "Sending..." state. I've already reported this to customer support. Symptom of JMAP, or just a run-of-the-mill bug somewhere?