Co-founder here, we are bootstrapping this new thing called Missive.

It is a collaborative email client, we have been beta testing the web version for the past two months and now just released the OS X app.

Request an invite here https://missiveapp.com/#request-an-invite and ping us @missiveapp or info@missiveapp.com to get in.

I'm happy to answer your questions.

Does it requires a login, and/or my Gmail/Yahoo/etc. emails have to pass thru a third party server (yours)?

Edit:

Answered on help: "Every connection between Missive clients and our servers is encrypted using the Transport Layer Security standard (TLS). This also applies to connections between our servers and Gmail when we fetch your emails."

Thanks, but I pass.

Yes, it does pass thru our servers. That's how we can create shared conversations between members of the same team.

Our email client consumes data from our API.