I was just looking for something like this at work a few days ago! I'll be trying it out first thing on Monday.
// Does this mean I can bill my hour of browsing HN today as research time?
Does that problem solving thinking ever stop?
How does this compare with JMAP?
JMAP is an alternative protocol to IMAP while EmailEngine is basically a proxy. If you want to build a new Outlook or Thunderbird you probably have to connect to email servers directly and speak IMAP or JMAP. If you want to easily integrate a lot of email accounts with your existing system and only care about basic info (like notifications about new emails etc) then EmailEngine is easier to use as it handles all the hard work itself.