I'm looking forward to seeing how Front stacks up when ready! :D Email clients seems to be a strange place where you can get acquired before you even launch... so maybe we'll never see a public product if you innovate too much! :D
I'm surprised that Mailpile[0] wasn't mentioned at all. It's something that I'm watching very closely.
Is there nothing to build on top of? A "e-mail" dev framework (open source if possible) with hooks so that you can focus on only front-end, or something similar?
that's an interesting question! The thing is that there is so much "plumbing" to do that a lot of the value is in the backend. Since it cannot be used by many many projects (we won't build thousands of email clients)the market for this open source model seems too small. My 2 cents.