The future is coming called Inbox, they are a open-source "next-generation email platform" have a look at: https://www.inboxapp.com/
You can read more about it on the The Next Web site: http://thenextweb.com/insider/2014/07/07/inbox-launches-open-source-email-platform-replace-legacy-protocols/
I think it would be a great alternative which puts Blesta another step forward, and they are doing a SaaS version soon, so if this was a option in Blesta maybe a option for Hosted or SaaS.
Ps: I think Cody might like the Javascript SDK haha.